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Unit 4 Uncertainty Inference - Continuous Wang, Yuan-Kai, 王元凱 [email protected] http://www.ykwang.tw Department of Electrical Engineering, Fu Jen Univ. 輔仁大學電機工程系 2006~2011 Bayesian Networks Fu Jen University Department of Electrical Engineering Wang, Yuan-Kai Copyright Reference this document as: Wang, Yuan-Kai, “Uncertainty Inference - Continuous," Lecture Notes of Wang, Yuan-Kai, Fu Jen University, Taiwan, 2011.

04 Uncertainty inference(continuous)

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Page 1: 04 Uncertainty inference(continuous)

Unit 4 Uncertainty Inference - Continuous

Wang Yuan-Kai 王元凱ykwangmailsfjuedutw

httpwwwykwangtw

Department of Electrical Engineering Fu Jen Univ輔仁大學電機工程系

2006~2011

Bayesian Networks

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Reference this document as Wang Yuan-Kai ldquoUncertainty Inference - Continuous

Lecture Notes of Wang Yuan-Kai Fu Jen University Taiwan 2011

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Goal of this Unit Review basic concepts of

statistics in terms of Image processing Pattern recognition

2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Related Units Previous unit(s) Probability Review

Next units Uncertainty Inference (Discrete) Uncertainty Inference (Continuous)

3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Self-Study Artificial Intelligence a modern

approach Russell amp Norvig 2nd Prentice Hall

2003 pp462~474 Chapter 13 Sec 131~133

統計學的世界 墨爾著鄭惟厚譯 天下文化2002

深入淺出統計學 D Grifiths 楊仁和譯2009 Orsquo Reilly

4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

55

Contents1 Gaussian helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62 Gaussian Mixtures 363 Linear Gaussian 804 Sampling 925 Markov Chain 1026 Stochastic Process 1067 Reference helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 114

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

6

1 Gaussian Distribution 11 Univariate Gaussian 12 Bivariate Gaussian 13 Multivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

7

Why Should We CareGaussians are as natural as

Orange Juice and SunshineWe need them to understand

mixture modelsWe need them to understand

Bayes Optimal ClassifiersWe need them to understand

Bayes Network

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

王元凱 Unit - Uncertainty Inference (Continuous) p

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

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once

ntra

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2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

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ntra

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EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

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od C

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EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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王元凱 Unit - Uncertainty Inference (Continuous) p

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

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od C

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n C

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EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

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Red Blood Cell Volume

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EM ITERATION 15

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33 34 35 36 37 38 39 437

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Red Blood Cell Volume

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ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 2: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Goal of this Unit Review basic concepts of

statistics in terms of Image processing Pattern recognition

2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Related Units Previous unit(s) Probability Review

Next units Uncertainty Inference (Discrete) Uncertainty Inference (Continuous)

3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Self-Study Artificial Intelligence a modern

approach Russell amp Norvig 2nd Prentice Hall

2003 pp462~474 Chapter 13 Sec 131~133

統計學的世界 墨爾著鄭惟厚譯 天下文化2002

深入淺出統計學 D Grifiths 楊仁和譯2009 Orsquo Reilly

4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

55

Contents1 Gaussian helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62 Gaussian Mixtures 363 Linear Gaussian 804 Sampling 925 Markov Chain 1026 Stochastic Process 1067 Reference helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 114

王元凱 Unit - Uncertainty Inference (Continuous) p

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6

1 Gaussian Distribution 11 Univariate Gaussian 12 Bivariate Gaussian 13 Multivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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7

Why Should We CareGaussians are as natural as

Orange Juice and SunshineWe need them to understand

mixture modelsWe need them to understand

Bayes Optimal ClassifiersWe need them to understand

Bayes Network

王元凱 Unit - Uncertainty Inference (Continuous) p

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8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

王元凱 Unit - Uncertainty Inference (Continuous) p

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

王元凱 Unit - Uncertainty Inference (Continuous) p

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

王元凱 Unit - Uncertainty Inference (Continuous) p

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

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tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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Example Approximate reasoning for

Bayesian networks TBU

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5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 3: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Related Units Previous unit(s) Probability Review

Next units Uncertainty Inference (Discrete) Uncertainty Inference (Continuous)

3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Self-Study Artificial Intelligence a modern

approach Russell amp Norvig 2nd Prentice Hall

2003 pp462~474 Chapter 13 Sec 131~133

統計學的世界 墨爾著鄭惟厚譯 天下文化2002

深入淺出統計學 D Grifiths 楊仁和譯2009 Orsquo Reilly

4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

55

Contents1 Gaussian helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62 Gaussian Mixtures 363 Linear Gaussian 804 Sampling 925 Markov Chain 1026 Stochastic Process 1067 Reference helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 114

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6

1 Gaussian Distribution 11 Univariate Gaussian 12 Bivariate Gaussian 13 Multivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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7

Why Should We CareGaussians are as natural as

Orange Juice and SunshineWe need them to understand

mixture modelsWe need them to understand

Bayes Optimal ClassifiersWe need them to understand

Bayes Network

王元凱 Unit - Uncertainty Inference (Continuous) p

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8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

王元凱 Unit - Uncertainty Inference (Continuous) p

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

王元凱 Unit - Uncertainty Inference (Continuous) p

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

王元凱 Unit - Uncertainty Inference (Continuous) p

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

王元凱 Unit - Uncertainty Inference (Continuous) p

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 4: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

Self-Study Artificial Intelligence a modern

approach Russell amp Norvig 2nd Prentice Hall

2003 pp462~474 Chapter 13 Sec 131~133

統計學的世界 墨爾著鄭惟厚譯 天下文化2002

深入淺出統計學 D Grifiths 楊仁和譯2009 Orsquo Reilly

4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

55

Contents1 Gaussian helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62 Gaussian Mixtures 363 Linear Gaussian 804 Sampling 925 Markov Chain 1026 Stochastic Process 1067 Reference helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 114

王元凱 Unit - Uncertainty Inference (Continuous) p

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6

1 Gaussian Distribution 11 Univariate Gaussian 12 Bivariate Gaussian 13 Multivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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7

Why Should We CareGaussians are as natural as

Orange Juice and SunshineWe need them to understand

mixture modelsWe need them to understand

Bayes Optimal ClassifiersWe need them to understand

Bayes Network

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

王元凱 Unit - Uncertainty Inference (Continuous) p

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

王元凱 Unit - Uncertainty Inference (Continuous) p

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

王元凱 Unit - Uncertainty Inference (Continuous) p

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

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Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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Example ndash Clustering (34)

x and y are dependent

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Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

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30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 5: 04 Uncertainty inference(continuous)

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55

Contents1 Gaussian helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62 Gaussian Mixtures 363 Linear Gaussian 804 Sampling 925 Markov Chain 1026 Stochastic Process 1067 Reference helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 114

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6

1 Gaussian Distribution 11 Univariate Gaussian 12 Bivariate Gaussian 13 Multivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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7

Why Should We CareGaussians are as natural as

Orange Juice and SunshineWe need them to understand

mixture modelsWe need them to understand

Bayes Optimal ClassifiersWe need them to understand

Bayes Network

王元凱 Unit - Uncertainty Inference (Continuous) p

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8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

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10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 6: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

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6

1 Gaussian Distribution 11 Univariate Gaussian 12 Bivariate Gaussian 13 Multivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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7

Why Should We CareGaussians are as natural as

Orange Juice and SunshineWe need them to understand

mixture modelsWe need them to understand

Bayes Optimal ClassifiersWe need them to understand

Bayes Network

王元凱 Unit - Uncertainty Inference (Continuous) p

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8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

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9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

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10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

王元凱 Unit - Uncertainty Inference (Continuous) p

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

王元凱 Unit - Uncertainty Inference (Continuous) p

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

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22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 7: 04 Uncertainty inference(continuous)

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7

Why Should We CareGaussians are as natural as

Orange Juice and SunshineWe need them to understand

mixture modelsWe need them to understand

Bayes Optimal ClassifiersWe need them to understand

Bayes Network

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8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

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9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

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10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 8: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

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8

11 Univariate Gaussian Univaraite Gaussian is a

Gaussian with only one variable

2exp

21)(

2xxp

1]Var[ X0][ XE

Unit-variance Gaussian

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9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

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10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

王元凱 Unit - Uncertainty Inference (Continuous) p

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

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22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 9: 04 Uncertainty inference(continuous)

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9

General Univariate Gaussian

2

2

2)(exp

21)(

xxp

2]Var[ XμXE ][

=100

=15

bull It is also called Normal distributionbull Bell-shape curve

王元凱 Unit - Uncertainty Inference (Continuous) p

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10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 10: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

10

Normal Distribution

bull X ~ N()bull ldquoX is distributed as a Gaussian with

parameters and 2rdquobull In this figure X ~ N(100152)

=100

=15

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

王元凱 Unit - Uncertainty Inference (Continuous) p

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

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22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 11: 04 Uncertainty inference(continuous)

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11

A Live Demo and are two parameters of the

Gaussian Position parameter Shape parameter

Demo

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 12: 04 Uncertainty inference(continuous)

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12

Cumulative Distribution Function

x xxdxedxxpxF

22 2)(

21)()(

Density Function for the Standardized Normal Variate

0

005

01

015

02

025

03

035

04

045

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Den

sity

Cumulative Distribution Function for a Standardized Normal Variate

0010203040506070809

1

-5 -4 -3 -2 -1 0 1 2 3 4 5

Standard Deviations

Prob

abilt

y

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

王元凱 Unit - Uncertainty Inference (Continuous) p

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

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22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 13: 04 Uncertainty inference(continuous)

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13

The Error Functionbull Assume X ~ N(01)bull Define ERF(x) = P(Xltx)

= Cumulative Distribution of X

x

z

dzzpxERF )()(

x

z

dzz2

exp21 2

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 14: 04 Uncertainty inference(continuous)

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14

Using The Error FunctionAssume X ~ N(01)P(Xltx| 2) = )( 2

xERF

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

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Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 15: 04 Uncertainty inference(continuous)

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15

The Central Limit TheoremIf (X1 X2 hellip Xn) are iid continuous

random variablesThen define As n p(z) Gaussian with

mean E[Xi] and variance Var[Xi]

n

iin x

nxxxfz

121

1)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

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22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 16: 04 Uncertainty inference(continuous)

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16

Example ndashZero Mean Gaussian amp Noise Zero mean Gaussian N(0) Usually used as noise model in

images An image f(xy) with noise N(0)

means f(xy) = g(xy) + N(0)

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17

12 Bivariate Gaussian

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

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tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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Example Approximate reasoning for

Bayesian networks TBU

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5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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Graphical View of Stochastic Process

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Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 17: 04 Uncertainty inference(continuous)

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17

12 Bivariate Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 18: 04 Uncertainty inference(continuous)

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18

The Formula

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

2

1

μ

2

1 vector randomFor XX

X

22

21

1212

Σ

If X N( )

王元凱 Unit - Uncertainty Inference (Continuous) p

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19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

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22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 19: 04 Uncertainty inference(continuous)

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

19

Gaussian Parameters )()(exp

||||2

1)( 121

21 μXμXXp T Σ

Σ

amp are Gaussianrsquos parameters

2

1

μ

22

21

1212

Σ

Position parameter Shape parameter

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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Example ndash Clustering (34)

x and y are dependent

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Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

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Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 20: 04 Uncertainty inference(continuous)

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20

Graphical Illustration

1

2

1

2

X1

X2p(X)

X1

Position parameter Shape parameter 1 2

Principal axis

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 21: 04 Uncertainty inference(continuous)

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21

General Gaussian

X1

X2

2

1

μ

22

21

1212

Σ

X1

X2

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 22: 04 Uncertainty inference(continuous)

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22

Axis-Aligned Gaussian X1 and X2 are independent or

uncorrelated

X1

X2

2

1

μ

22

12

00

Σ

X1

X2

σ1 gt σ2 σ1 lt σ2

王元凱 Unit - Uncertainty Inference (Continuous) p

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 23: 04 Uncertainty inference(continuous)

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23

Spherical Gaussian

2

2

00

Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

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30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 24: 04 Uncertainty inference(continuous)

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24

Degenerated Gaussians

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

0|||| Σ

X1

X2

2

1

μ

王元凱 Unit - Uncertainty Inference (Continuous) p

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25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

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once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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Example Approximate reasoning for

Bayesian networks TBU

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5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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Graphical View of Stochastic Process

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Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 25: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

25

Example ndash Clustering (14) Given a set of data points in a 2D

space Find the Gaussian distribution of

those points

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

王元凱 Unit - Uncertainty Inference (Continuous) p

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27

Example ndash Clustering (34)

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

王元凱 Unit - Uncertainty Inference (Continuous) p

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 26: 04 Uncertainty inference(continuous)

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26

Example ndash Clustering (24) A 2D space example Face verification of a person We use 2 features to verify the person Size Length

We get 1000 faceimages of the person

Each image has 2 features a data pointin the 2D space

Find the mean and range of 2 features

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

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30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 27: 04 Uncertainty inference(continuous)

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27

Example ndash Clustering (34)

x and y are dependent

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 28: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

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28

Example ndash Clustering (44)

x and y are almost independent

x and y are dependent

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13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

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Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 29: 04 Uncertainty inference(continuous)

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29

13 Multivariate Gaussian

Tm

m

XXX

X

XX

)( vector randomFor 212

1

X

If X N( )

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 30: 04 Uncertainty inference(continuous)

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30

Gaussian Parameters

Position parameter Shape parameter

amp are Gaussianrsquos parameters

m

2

1

μ

mmm

m

m

221

222

21

11212

Σ

)()(exp||||)2(

1)( 121

21

2μxΣμx

Σx T

mp

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 31: 04 Uncertainty inference(continuous)

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31

Axis-Aligned Gaussians

m

2

1

μ

m

m

2

12

32

22

12

00000000

000000000000

Σ

X1

X2

X1

X2

王元凱 Unit - Uncertainty Inference (Continuous) p

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

王元凱 Unit - Uncertainty Inference (Continuous) p

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

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once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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Example Approximate reasoning for

Bayesian networks TBU

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5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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Graphical View of Stochastic Process

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Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 32: 04 Uncertainty inference(continuous)

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32

Spherical Gaussians

m

2

1

μ

2

2

2

2

2

00000000

000000000000

Σ

x1

x2

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 33: 04 Uncertainty inference(continuous)

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33

Degenerate Gaussians

m

2

1

μ 0|||| Σ

x1

x2

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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王元凱 Unit - Uncertainty Inference (Continuous) p

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 34: 04 Uncertainty inference(continuous)

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34

Example ndash3-Variate Gaussian (12)

3

2

1

μ

32

3231

2322

21

131212

Σ

)()(exp||||)2(

1)( 121

21

23 μxΣμx

Σx Tp

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35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 35: 04 Uncertainty inference(continuous)

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

35

Example ndash3-Variate Gaussian (22)

Assume a simple case ij=0 if inej

32

22

12

000000

Σ

)()(exp||||)2(

1)( 121

21

23

μxΣμxΣ

x Tp

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 36: 04 Uncertainty inference(continuous)

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36

2 Gaussian Mixture Modelbull What is Gaussian Mixture

bull 2 Gaussians are mixed to be a pdfbull Why Gaussian Mixture

bull Single Gaussian is not enough Usually the distribution of your data

is assumed as one Gaussian Also called unimodal Gaussian

However sometimes the distribution of data is not a unimodal Gaussian

王元凱 Unit - Uncertainty Inference (Continuous) p

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

王元凱 Unit - Uncertainty Inference (Continuous) p

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

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once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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Example Approximate reasoning for

Bayesian networks TBU

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5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 37: 04 Uncertainty inference(continuous)

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37

Why Is Unimodal Gaussian not Enough (13)

A univariate example Histogram of an image

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 38: 04 Uncertainty inference(continuous)

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38

Why Is Unimodal Gaussian not Enough (23)

Bivariate example

One Gaussian PDF

王元凱 Unit - Uncertainty Inference (Continuous) p

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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王元凱 Unit - Uncertainty Inference (Continuous) p

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 39: 04 Uncertainty inference(continuous)

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39

Why Is Unimodal Gaussian not Enough (33)

To solve it

Mixture of Three Gaussians

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 40: 04 Uncertainty inference(continuous)

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40

Gaussian Mixture Model(GMM)

21 Combine Multiple Gaussians

22 Formula of GMM23 Parameter Estimation

of GMM

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 41: 04 Uncertainty inference(continuous)

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41

21 Combine Multiple Gaussians

1

2 1 2

1 1( ) exp22

Tnp x x x

11 1 12 1 2

1

12 2 22 1 2

2

1 1( ) exp22

1 1 exp22

Tn

Tn

p x x x

x x

bull Unimodal Gaussian (Single Gaussian)

bull Multi-modal Gaussians (Multiple Gaussians)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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58

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 42: 04 Uncertainty inference(continuous)

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42

Combine 2 Gaussians (14) Suppose Two Gaussians in 1-dimension

1 21 2( ) ( | ) ( | )p x p x p x

2

2

1| exp 1222

ii i

ii

xp x i

p(x) = p(x | C1) + p(x | C2)

p(x|Ci)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

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Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

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n C

once

ntra

tion

EM ITERATION 3

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

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ell H

emog

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n C

once

ntra

tion

EM ITERATION 10

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

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ell H

emog

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n C

once

ntra

tion

EM ITERATION 25

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0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

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tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

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Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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Example Approximate reasoning for

Bayesian networks TBU

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5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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Graphical View of Stochastic Process

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Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 43: 04 Uncertainty inference(continuous)

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43

1-D Example (24)

2

2

2

2

1 ( 4)( ) exp( )2 032 03

1 ( 64) exp( )2 052 05

xp x

x

1=4 1=032=64 2=05

1=062=04

Given x=52

2

2

2

1 (5 4)( 5) exp( )2 032 03

1 (5 64) exp( )2 052 05

p x

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 44: 04 Uncertainty inference(continuous)

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44

Combine 2 Gaussians (34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

Gaussian Mixture

N(01)=p(x|01)N(31)=p(x|31)

p(x)=p(x|01)+p(x|31)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 45: 04 Uncertainty inference(continuous)

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45

Combine 2 Gaussians (44)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x)=p(x|01)+p(x|34)

王元凱 Unit - Uncertainty Inference (Continuous) p

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

王元凱 Unit - Uncertainty Inference (Continuous) p

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 46: 04 Uncertainty inference(continuous)

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46

Combine 2 Gaussians with Weights (13)

If p(x) = frac12 p(x | C1) + frac12 p(x | C2)

p(x|Ci)dx = 1 p(x)dx = p(x|C1)dx + p(x|C2)dx = 1 + 1 = 2

p(x) = p(x | C1) + p(x | C2)

p(x)dx = frac12 p(x|C1)dx + frac12 p(x|C2)dx = 1

If p(x) = 1 p(x | C1) + 2 p(x | C2) 1+2=1 p(x)dx = 1 p(x|C1)dx + 2 p(x|C2)dx = 1

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 47: 04 Uncertainty inference(continuous)

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47

Combine 2 Gaussians with Weights (23)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05

x

p(x)

N(01) N(31)

2 Gaussians

N(01)=p(x|01)N(31)=p(x|31)

p(x) = frac12 p(x|01)+ frac12 p(x|31)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01) N(31)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

王元凱 Unit - Uncertainty Inference (Continuous) p

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

王元凱 Unit - Uncertainty Inference (Continuous) p

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 48: 04 Uncertainty inference(continuous)

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48

Combine 2 Gaussians with Weights (33)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

052 Gaussians

x

p(x)

N(01)

N(34)

N(01)=p(x|01)N(34)=p(x|34)

p(x) = frac12 p(x|01)+ frac12 p(x|34)

-4 -3 -2 -1 0 1 2 3 4 5 6 70

005

01

015

02

025

03

035

04

045

05Gaussian Mixture

x

p(x)

N(01)

N(34)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

王元凱 Unit - Uncertainty Inference (Continuous) p

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 49: 04 Uncertainty inference(continuous)

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49

Combine 2 Gaussians with Different Mean Distances (12)

Suppose Two Gaussians in 1D

1 21 1

1 22 2( ) ( | ) ( | )p x p x p x

Let = 1 Let =

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 50: 04 Uncertainty inference(continuous)

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50

=1 =2

=3 =4

Combine 2 Gaussians with Different Mean Distances (22)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 51: 04 Uncertainty inference(continuous)

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51

Combine 2 Gaussians with Different Weights (12)

Suppose Two Gaussians in 1D

1 21 2( ) 075 ( | ) 025 ( | )p x p x p x

Let = 1 Let =

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

王元凱 Unit - Uncertainty Inference (Continuous) p

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 52: 04 Uncertainty inference(continuous)

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52

=1 =2

=3 =4

Combine 2 Gaussians with Different Weights (22)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 53: 04 Uncertainty inference(continuous)

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53

2D Gaussian Combination (12)

1 1 1 2 2 1

4 0 4 0( | ) (00) ( | ) (03)

0 4 0 4p x C p x C

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54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

57

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 54: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

54

2D Gaussian Combination (22)

p(x) = p(x|C1) + p(x|C2)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

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57

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58

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22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 55: 04 Uncertainty inference(continuous)

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55

More Gaussians As no of Gaussians M

increases it can represent any possible density By adjusting M and of

each Gaussians

1

1

( ) ( | )

( | )

M

i iiM

i i ii

p x p x C

p x

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

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ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

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43

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Red Blood Cell Volume

Red

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tion

EM ITERATION 3

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73

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74

33 34 35 36 37 38 39 437

38

39

4

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n C

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tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

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43

44

Red Blood Cell Volume

Red

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emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

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emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

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od C

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emog

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n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 56: 04 Uncertainty inference(continuous)

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56

-5 0 5 100

05

1

15

2

Component Modelsp(

x)

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

5 Gaussians

王元凱 Unit - Uncertainty Inference (Continuous) p

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57

王元凱 Unit - Uncertainty Inference (Continuous) p

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58

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

王元凱 Unit - Uncertainty Inference (Continuous) p

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

王元凱 Unit - Uncertainty Inference (Continuous) p

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

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33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

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ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

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ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

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ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

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n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 57: 04 Uncertainty inference(continuous)

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

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73

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74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

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78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 58: 04 Uncertainty inference(continuous)

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 59: 04 Uncertainty inference(continuous)

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59

22 Formula of GMM A Gaussian mixture model

(GMM) is a linear combinationof M Gaussians

M

iii Cxpxp

1) |()(

bull P(x) is the probability of a point xbullx=(Cb Cr) or (RGB) or

bull i is mixing parameter (weight)bull p(x|Ci) is a Gaussian function

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 60: 04 Uncertainty inference(continuous)

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60

Comparison of Formula

In GMM p(x|Ci) means the probability of x in the i Gaussian component

1

2 1 21 1( ) exp

22

Tnp x x x

1

12 1 2

1

( ) ( | )

1exp22

M

i ii

MTi

i i ini i

p x p x C

x x

Gaussian

GMM

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61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

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62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

王元凱 Unit - Uncertainty Inference (Continuous) p

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

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80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

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81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

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84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

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89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

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90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

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92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 61: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

61

Two Constraints of GMMbull i

bull p(x|Ci)bull It is normalized bull ie p(x|Ci)dx = 1

1 0 and 11

M

iii

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

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83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 62: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

62

The Problem (15) Now we know any density can be

obtained by Gaussian mixture Given the mixture function we can

plot its density But in reality what we need to do

in computer is We get a lot of data point =xj Rn

j=1hellipN with unknown density Can we find the mixture function of

these data points

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

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43

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n C

once

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tion

EM ITERATION 3

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73

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74

33 34 35 36 37 38 39 437

38

39

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n C

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ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

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n C

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ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

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39

4

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n C

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ntra

tion

EM ITERATION 25

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77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 63: 04 Uncertainty inference(continuous)

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63

-5 0 5 100

05

1

15

2

Component Models

p(x)

5 Gaussians

-5 0 5 100

01

02

03

04

05

Mixture Model

x

p(x)

Histograms of =xj Rn j=1hellipN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

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ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

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73

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

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n C

once

ntra

tion

EM ITERATION 10

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75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

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85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

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105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

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107

Graphical View of Stochastic Process

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 64: 04 Uncertainty inference(continuous)

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64

The Problem (35) To find the mixture function

means to estimate the parameters of the mixture function Mixing parameters Gaussian component densities Mean vector i

Covariance matrix i Number of components M

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

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69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 65: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

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65

The Problem (45)

1D Gaussian 2D Gaussian 3D Gaussian 1 2 3

() 1 3 6Total 2 5 9

1D GMM 2D GMM 3D GMM M M M 1 M 2 M 3 M

() 1 M 3 M 6 MTotal 3M 6M 10M

GMM with M Gaussians

A GaussianNo of Parameters

王元凱 Unit - Uncertainty Inference (Continuous) p

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66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

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70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

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79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

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82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

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86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

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87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

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88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

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94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 66: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

66

The Problem (55) That is given xj Rn j=1hellipN

M

iiii xpxp

111 ) |()(

M

iiii xpxp

122 ) |()(

M

iiiNiN xpxp

1) |()(

Usually we use i to denote (i i)

M

iii xpxp

1) |()(

Solve i i i

Also called parameter estimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 67: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

67

23 Parameter Estimation Given Fixed M Data =xj Rn j=1hellipN We may calculate the histogram of

We want to find the parameters = (1 M 1 M 1 M)that best fit the histogram of data

Examples 1-D example xj R1

Two 2-D examples xj R2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 68: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

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68

1-D Example=15 -02 14 18 Histogram

bullNx=-25=10bullbullNx=15=40bull

2

2

1 ( 15)( ) exp( )2 132 13xp x

=15 =13

ParameterEstimation

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 69: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

69

(Izenman ampSommer)

(Basford et al)

M=3

M=7M=7

M=4(equal variances)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

70

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

2-D Example=(345402)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

71

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 1

Initialization

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 70: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

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33 34 35 36 37 38 39 437

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39

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44ANEMIA PATIENTS AND CONTROLS

Red Blood Cell Volume

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tion

2-D Example=(345402)

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71

33 34 35 36 37 38 39 437

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39

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41

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emog

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n C

once

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tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

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39

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tion

EM ITERATION 3

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73

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74

33 34 35 36 37 38 39 437

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EM ITERATION 10

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75

33 34 35 36 37 38 39 437

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tion

EM ITERATION 15

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76

33 34 35 36 37 38 39 437

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39

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tion

EM ITERATION 25

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

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39

4

41

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Red Blood Cell Volume

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ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

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93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

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96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

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97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

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113

Example - Video Facial expression recognition TBU

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

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117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 71: 04 Uncertainty inference(continuous)

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Red Blood Cell Volume

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once

ntra

tion

EM ITERATION 1

Initialization

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72

33 34 35 36 37 38 39 437

38

39

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EM ITERATION 3

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73

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74

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39

4

41

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Red Blood Cell Volume

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ntra

tion

EM ITERATION 10

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75

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38

39

4

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Red Blood Cell Volume

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ntra

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EM ITERATION 15

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76

33 34 35 36 37 38 39 437

38

39

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Red Blood Cell Volume

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ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

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n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 72: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

72

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 73: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

73

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 74: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

74

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 10

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 75: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

75

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 15

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 76: 04 Uncertainty inference(continuous)

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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

76

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

EM ITERATION 25

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

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100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

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101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

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103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

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104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

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106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

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107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

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108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

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109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

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111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

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112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

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115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

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116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 77: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

77

0 5 10 15 20 25400

410

420

430

440

450

460

470

480

490LOG-LIKELIHOOD AS A FUNCTION OF EM ITERATIONS

EM Iteration

Log-

Like

lihoo

d

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 78: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

78

33 34 35 36 37 38 39 437

38

39

4

41

42

43

44

Red Blood Cell Volume

Red

Blo

od C

ell H

emog

lobi

n C

once

ntra

tion

ANEMIA DATA WITH LABELS

Anemia Group

Control Group

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

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98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 79: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

79

Parameter Estimation of GMM

Two methods Maximum Likelihood Estimation

(MLE) Expectation Maximization (EM)

Discussed in Lecture Note 24

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 80: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

80

3 Linear Gaussian P(X) can belong to a distribution Ex Gaussian uniform Exponential

Gaussian mixture) P(Y|X) conditional probability Can the conditional probability

belong to a distribution Linear Gaussian describes The distribution of conditional

probability as Gaussian The dependence between random

variables

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

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110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 81: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

81

- +

N(y)

y

From Gaussian to Linear Gaussian (12)

If two variables x and y has linearrelationship we say y = ax + b a and b are parameters

If y belongs to Gaussian distribution y ~ N( ) = N(y ) But y = ax+b ax+b ~ N( ) = N(ax+b ) But we can write

N(y ax+b )

y becomes a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

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113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

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114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 82: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

82

Linear Gaussian=N(yax+b ) The meaning of linear Gaussian

N(y ax+b )

-3 - + +3

N(y)

y

bull When y=ax+b N(y) is the maximum probability

bull However yax+boccurs

bullwith lower probability bulldecayed as in Gaussian distributionax+b

=

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 83: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

83

P(y|x) = N(yax+b ) P(Xj=y|Xi=x)=P(y|x) If P(y|x)=N(y ax+b ) Xj varies linearly with Xi With Gaussian uncertainty Standard deviation is fixed

2

2

2))((exp

21

)(

)|(

baxy

baxyN

xXyXP ij

XiXj

P(Xj | Xi)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 84: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

84

Example 1 (12) Illumination change of an image

g(xy) =af(xy)+b

f(xy) g(xy)

g =af+b

bullTwo kinds of illumination change(same ab)bullReal light change g1bullChanged by image processing software g2

bullg1 = g2 NobullBecause of noise g1 is a random variable

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 85: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

85

Example 1 (22) Illumination change of an image

f(xy) g1(xy)

g1 =af+b

bullBut g1 is a random variablebullIt means g1 undergoes a noisebullg1 ~ af + b + N(0) = N(af+b )bullOr P(g1|f) = N(af+b )

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 86: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

86

Extension Linear Transform X and Y are two vectors Y = (y1 y2 hellip ym)T

X = (x1 x2 hellip xm)T

X and Y are linearly dependent Y = AX + B Linear transform

If Y becomes a random vector P(Y|X)=N(Y AX+B sum)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 87: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

87

Example 2 (15) Illumination change of color image

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

F(xy) G(xy)

G =AF+B

bullF(xy)=(rF(xy) gF(xy) bF(xy)T

bullG(xy)=(rG(xy) gG(xy) bG(xy)T

G =AF+B

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 88: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

88

Example 2 (25) A simple case of G=AF+B aij=0 if inej

RG=a11RF+b1 GG=a22GF+b2 BG=a33BF+b3

001

100030002

F

F

F

G

G

G

bgr

bgr

3

2

1

333231

232221

131211

bbb

bgr

aaaaaaaaa

bgr

F

F

F

G

G

G

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 89: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

89

Example 2 (35) If G has noises

F(xy) G1(xy)

G1 =AF+B

bullG1(xy) is a random vectorbullIt means G1 undergoes a noisebullG1 ~ AF + B + N(0sum)

= N(AF+B sum)bullOr P(G1|F) = N(AF+B sum)

333231

232221

131211

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 90: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

90

Example 2 (45) G1 ~ N(AF+B sum) N is a multivariate Gaussian (3-D)

333231

232221

131211

)()(exp||||2

1)( 121

21 μXμXXp T Σ

Σ

3333231

2232221

1131211

bbagarabbagarabbagara

BAF

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 91: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

91

Example 2 (55) Assume a simple case aij=0 if inej ij=0 if inej

Then

P(rG|rF) = N(a11rF+b1 1) P(gG|gF) = N(a21gF+b2 2) P(bG|bF) = N(a31bF+b3 3)

100030002

A

200080004

333

222

111

3333231

2232221

1131211

bbabgabra

bbagarabbagarabbagara

BAF

F

F

F

FFF

FFF

FFF

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 92: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

92

4 Sampling Generate N samples S from P(X) S=(s1s2 hellip sN)

X can be a random variable or a random vector If X=x si=xi

If X=(x1x2hellipxn) si=(x1ix2

ihellipxni)

Why generate N samples Estimate probabilities by frequencies

NxXxXP

with samples)(

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 93: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

93

Example (12) A simple example coin toss Tossing the coin get head or tail It is a Boolean random variable coin = head or tail Random variable but not

random vector If it is unbiased coin head and tail

have equal probability A prior probability distribution

P(Coin) = lt05 05gt Uniform distribution

But we do not know it is unbiased

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 94: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

94

Example (22) Sampling in this example

= flipping the coin many times N eg N=1000 times Ideally 500 heads 500 tails P(head) = 5001000=05

P(tail) = 5001000=05 Practically 5001 heads 499 tails P(head) = 5011000=0501

P(tail) = 4991000=0499 By the sampling we can

estimate the probability distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 95: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

95

Sampling (Math) For a Boolean random variable X P(X) is prior distribution

= ltP(x) P(x)gt Using a sampling algorithm to

generate N samples Say N(x) is the number of samples

that x is true N(x) of x is false

)(ˆ)( )(ˆ)( xPN

xNxPN

xN

)()(lim )()(lim xPN

xNxPN

xNNN

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 96: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

96

Sampling Algorithm It is the algorithm to Generate samples from a known

probability distribution Estimate the approximate

probability How does a sampling algorithm

generate a sample CC++ rand() Return 0 ~ RAND_MAX (32767)

Java random()

P

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 97: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

97

A Sampling Algorithm of the Coin Toss

Flip the coin 1000 times int coin_face

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2)

coin_face = 1else coin_face = 0

What kind of distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 98: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

98

Sampling Algorithms for Many RVs (12)

3 Boolean random variables X Y Z (X=1 Y=0 Z=0) is called a sample int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX2) Y = 1

else Y = 0 if (rand() gt RAND_MAX2) Z = 1

else Z = 0 X Y Z are all

uniform distribution

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 99: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

99

Sampling Algorithms for Many RVs (22)

Y Z are not uniform distribution P(Y)=lt067 033gt

P(Z)=lt025075gt int X Y Z

for (i=0 ilt1000 i++) if (rand() gt RAND_MAX2) X = 1

else X = 0if (rand() gt RAND_MAX3) Y = 1

else Y = 0 if (rand() gt RAND_MAX4) Z = 1

else Z = 0

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 100: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

100

Various Sampling Algorithms For more complex P(X) we need

more complex sampling algo Stochastic simulation Direct Sampling Rejection sampling Reject samples disagreeing with

evidence Likelihood weighting Use evidence to weight samples

Markov chain Monte Carlo (MCMC) Also called Gibbs sampling

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 101: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

101

Example Approximate reasoning for

Bayesian networks TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 102: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

102

5 Markov Chain Markov Assumption Each state at time t only

depends on the state at time t-1

Ex The weather today only depends on the weather of yesterday

(Andrei Andreyevich Markov)

X1 X2 X3

t=1 t=2 t=3

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 103: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

103

Deterministic vs Non-Deterministic

Deterministic patterns Traffic light FSMs hellip

Non-Deterministic patterns Weather Speech Tracking hellip

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 104: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

104

Example ndashWeather Prediction (12)

Only 3 possible weather states Sunny Cloudy Rainy

Transition Matrix A=Pr( today | yesterday)

Weather Today Sunny Cloudy Rainy

Sunny 05 025 025 Cloudy 0375 0125 0375

Weather

Yesterday Rainy 0125 0625 0375

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 105: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

105

Example ndashWeather Prediction (22)

Suppose we know the weather of previous days t=1 rainy t=2 sunny t=3 sunny t=4 cloudy

Predict the weather of day t=5

X5

t=5

X1

t=1

R

X2

t=2

S

X3

t=3

S

X4

t=4

C

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 106: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

106

6 Stochastic Process

Also called Random Process It is a collection of random

variables For each t in the index set T X(t) is a

random variable Usually t refers to time and X(t) is

the state of the process at time t X(t) can be discrete or continuous

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 107: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

107

Graphical View of Stochastic Process

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 108: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

108

Statistics of Stochastic Process

Mean of X(t) Variance standard deviation of X(t) Frequency distribution of X(t) P(X) Conditional probability of X(t)

P(X(t) | X(t-1))

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 109: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

109

Markov Chain A Markov chain is a stochastic

process where P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t)) or P(Xn+1 | Xn Xn-1 hellip X0)

= P(Xn+1 | Xn) Next state depends only on current

state Future and past are conditionally

independent given current

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 110: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

110

Higher-order Markov Chain Second-order Markov chain P(X(t+1) | X(t) X(t-1) hellip X(0))

= P(X(t+1) | X(t) X(t-1))

X1

t=1

X2

t=2

X3t=3

X4

t=4

Third-order n-order

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 111: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

111

Stationary Process The probability distribution of X is

independent of t

X1

t=1

X2

t=2

X3t=3

X4

t=4

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 112: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

112

Doubly Stochastic Process Hidden variable

Y1 Y3

X1 X2 X3

Y2

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 113: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

113

Example - Video Facial expression recognition TBU

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 114: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

114

7 Reference Moments

Hu M K [1962] ldquoVisual Pattern Recognition by Moment Invariantsrdquo IRE Trans Info Theory vol IT-8 pp 179-187

Gonzalez RC and R E Woods [2001] Digital Image Processing 2nd Prentice Hall pp659-660 672-675

L Rocha et al ldquoImage Moments-Based Structuring and Tracking of Objectsrdquo Proceedings of the XV Brazilian Symposium on Computer Graphics and Image Processing 2002

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 115: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

115

Reference Gaussian mixture

C M Bishop Neural Networks for Pattern Recognition Oxford University Press 1995

McLachlan and Peel Finite Mixture Models John Wiley amp Sons

Rennie ldquoA Short Tutorial on Using EM with Mixture Modelsrdquo MIT Tech Report 2004 httpwwwaimitedu peoplejrenniewritingmixtureEMpdf

Tomasi ldquoEstimating Gaussian Mixture Density with EM a tutorialrdquo Duke University

Y Weiss Motion segmentation using EM ndash a short tutorial 1997 httpwwwcshujiacil˜yweissemTutorialpdf

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 116: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

116

Reference Linear Gaussian

Russell amp Norvig Artificial Intelligence a modern approach 2nd Prentice Hall 2003Sec 143 pp501-503

Sampling RussellampNorvig Artificial Intelligence a modern

approach 2nd Prentice Hall 2003Sec 145 pp511-518

Stochastic process Probability Random variables and Random

Signal Principles 4e Peebles McGraw Hill 2001

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67

Page 117: 04 Uncertainty inference(continuous)

王元凱 Unit - Uncertainty Inference (Continuous) p

Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright

117

General References 統計學的世界鄭惟厚譯天下文化2002

Statistics concepts and controversies 5th D S Moore 2001

Sampling Chap 1-4 隨機程序與機率楊政穎等譯滄海

Probability Random variables and Random Signal Principles 4e Peebles McGraw Hill 2001 Moment Chap 3 Random process Chap 67