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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
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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
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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
Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright
23
Spherical Gaussian
2
2
00
Σ
X1
X2
2
1
μ
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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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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
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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
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Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright
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
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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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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
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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
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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)
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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
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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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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
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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
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)
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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
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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
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
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
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
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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
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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
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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))
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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
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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
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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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
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
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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
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
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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
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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
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
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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
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
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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
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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
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
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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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39
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41
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43
44
Red Blood Cell Volume
Red
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od C
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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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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
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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
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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
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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
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
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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
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)
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
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
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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
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
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
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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
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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
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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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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)(
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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
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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
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
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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
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
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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
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
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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
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
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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
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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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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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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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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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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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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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-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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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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33 34 35 36 37 38 39 437
38
39
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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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
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n C
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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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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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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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
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
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
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
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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
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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
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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
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)(
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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
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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
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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
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
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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
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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
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
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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
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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
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
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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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
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
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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
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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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)(
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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
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
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
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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
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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
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( )
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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
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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
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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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
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)
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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)
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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
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
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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
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
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 )
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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
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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)(
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
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
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
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
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
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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
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
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)
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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)
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)
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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
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
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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
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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
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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
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)(
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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
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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
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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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
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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)
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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
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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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
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 )
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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
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)(
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
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
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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
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
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
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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
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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
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
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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
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
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
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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 =
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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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
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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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
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
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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
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)
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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
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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
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
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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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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
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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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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
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
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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
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
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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
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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
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
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
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
Fu Jen University Department of Electrical Engineering Wang Yuan-Kai Copyright
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
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
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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)
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 =
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
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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
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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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
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
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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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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
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
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
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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
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
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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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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
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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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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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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)
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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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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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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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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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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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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
=
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 )
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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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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
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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
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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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
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
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
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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
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
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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
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
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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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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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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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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
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
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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
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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
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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
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
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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
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
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
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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
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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
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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
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
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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
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
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
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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
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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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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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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
Blo
od C
ell H
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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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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
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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
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
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
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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
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
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)
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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)
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
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
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
od C
ell H
emog
lobi
n C
once
ntra
tion
EM ITERATION 3
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73
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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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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
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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
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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
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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
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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
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
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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
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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
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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
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
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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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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
Blo
od C
ell H
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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
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
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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
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
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
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
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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
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
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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
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
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
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
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)
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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
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
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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
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
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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
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
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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
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
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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
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
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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
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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
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
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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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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
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
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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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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
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
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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
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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
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
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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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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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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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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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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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-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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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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33 34 35 36 37 38 39 437
38
39
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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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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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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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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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
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
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
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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
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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
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
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
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
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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 =
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
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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
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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
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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
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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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
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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
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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
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
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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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)
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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
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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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
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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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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
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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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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
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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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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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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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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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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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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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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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33 34 35 36 37 38 39 437
38
39
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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33 34 35 36 37 38 39 437
38
39
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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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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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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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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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
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
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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
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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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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
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)
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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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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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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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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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-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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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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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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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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33 34 35 36 37 38 39 437
38
39
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
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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
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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
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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
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
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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
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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
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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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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
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
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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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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)
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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
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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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
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
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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
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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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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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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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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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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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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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-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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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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33 34 35 36 37 38 39 437
38
39
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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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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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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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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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
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
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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
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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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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
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
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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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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
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
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
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
=
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
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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
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
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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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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
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)
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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)
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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
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
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
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
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
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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
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
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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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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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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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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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52
=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
Blo
od C
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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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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
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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
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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
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
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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
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
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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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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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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
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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)
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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
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
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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
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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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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
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
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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
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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
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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
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)
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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
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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
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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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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
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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
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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 =
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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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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
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
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
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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
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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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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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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)
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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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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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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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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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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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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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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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33 34 35 36 37 38 39 437
38
39
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
Blo
od C
ell H
emog
lobi
n C
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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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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- +
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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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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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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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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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
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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
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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
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)
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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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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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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
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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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33 34 35 36 37 38 39 437
38
39
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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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
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
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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)
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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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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
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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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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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33 34 35 36 37 38 39 437
38
39
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
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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
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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
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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
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)
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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)
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
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)
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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
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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33 34 35 36 37 38 39 437
38
39
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
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
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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
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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
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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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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
Blo
od C
ell H
emog
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n C
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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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
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
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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
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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 =
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)
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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
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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
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
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
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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
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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)
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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
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
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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
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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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33 34 35 36 37 38 39 437
38
39
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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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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33 34 35 36 37 38 39 437
38
39
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
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
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
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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
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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
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)
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
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
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
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
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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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33 34 35 36 37 38 39 437
38
39
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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33 34 35 36 37 38 39 437
38
39
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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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
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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)(
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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
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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
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)
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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 =
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
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
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
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
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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)
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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
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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
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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
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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
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
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
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)
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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
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
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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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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
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
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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 =
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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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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
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
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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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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
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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
Blo
od C
ell H
emog
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n C
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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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
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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 =
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
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
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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
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
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
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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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33 34 35 36 37 38 39 437
38
39
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
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
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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
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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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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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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
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
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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 =
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
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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
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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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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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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
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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
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
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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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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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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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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
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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
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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
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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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33 34 35 36 37 38 39 437
38
39
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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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
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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)
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
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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
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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)
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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
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
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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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33 34 35 36 37 38 39 437
38
39
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
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
=
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)(
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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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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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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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
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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
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
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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
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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
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
=
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
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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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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
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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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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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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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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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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
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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 =
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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
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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
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
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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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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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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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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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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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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
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=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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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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- +
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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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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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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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
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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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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
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
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
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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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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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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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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
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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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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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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
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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33 34 35 36 37 38 39 437
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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- +
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
王元凱 Unit - Uncertainty Inference (Continuous) p
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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
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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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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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
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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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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
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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
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
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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
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
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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
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
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
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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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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
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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33 34 35 36 37 38 39 437
38
39
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
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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
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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)
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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)
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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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
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
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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
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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
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
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
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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
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44
Red Blood Cell Volume
Red
Blo
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emog
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n C
once
ntra
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EM ITERATION 1
Initialization
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72
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39
4
41
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Red Blood Cell Volume
Red
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emog
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n C
once
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tion
EM ITERATION 3
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73
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39
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Red Blood Cell Volume
Red
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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
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39
4
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Red Blood Cell Volume
Red
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n C
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EM ITERATION 15
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76
33 34 35 36 37 38 39 437
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39
4
41
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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
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
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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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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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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
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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
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)
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
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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
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
=
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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
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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
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
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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
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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
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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)
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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
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)
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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
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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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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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
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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
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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
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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
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)
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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
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
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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
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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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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
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
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)
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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
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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 )
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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
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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))
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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
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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
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
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
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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
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
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
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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
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
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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
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
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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
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
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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
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
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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
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emog
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once
ntra
tion
2-D Example=(345402)
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33 34 35 36 37 38 39 437
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39
4
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Red Blood Cell Volume
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n C
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tion
EM ITERATION 1
Initialization
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39
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EM ITERATION 3
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EM ITERATION 10
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EM ITERATION 15
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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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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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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
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
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
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
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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
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
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
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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
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
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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
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Red Blood Cell Volume
Red
Blo
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emog
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once
ntra
tion
EM ITERATION 1
Initialization
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72
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39
4
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Red Blood Cell Volume
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tion
EM ITERATION 3
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39
4
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Red Blood Cell Volume
Red
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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
41
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43
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Red Blood Cell Volume
Red
Blo
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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
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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
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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
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
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
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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
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
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
42
43
44
Red Blood Cell Volume
Red
Blo
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ell H
emog
lobi
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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
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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
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
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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
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
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
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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
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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
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
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
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
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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
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
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
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)
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
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
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
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
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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
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
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
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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
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39
4
41
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EM ITERATION 3
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73
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EM ITERATION 10
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75
33 34 35 36 37 38 39 437
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39
4
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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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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
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
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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
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
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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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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
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
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
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Red Blood Cell Volume
Red
Blo
od C
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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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Red Blood Cell Volume
Red
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once
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tion
EM ITERATION 3
王元凱 Unit - Uncertainty Inference (Continuous) p
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73
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74
33 34 35 36 37 38 39 437
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39
4
41
42
43
44
Red Blood Cell Volume
Red
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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
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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
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
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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
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
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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
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
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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
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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
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
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
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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
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
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
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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
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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
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
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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
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
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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
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
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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
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
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
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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
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
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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
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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
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
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
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
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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
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
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
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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
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
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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
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
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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
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
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
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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
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
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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
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
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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
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
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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
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
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
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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
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
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
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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
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
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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
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
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
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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
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
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
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
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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
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
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
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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
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
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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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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