06_GENN004m_MATLABPrograms

7/29/2019 06_GENN004m_MATLABPrograms

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GENN004: Introduction to Computers 09-Feb-

MATLAB Programs

MATLAB Programs

Programmer-Defined Functions

Outline

The need for repetition

Counted Loops (for)

Conditional Loops (while)


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MATLAB Programs

Custom (User-Defined) Functions

So far we have used MATLABs built-in functions

rem, fix, sin, cos, etc

We have created programs that use various functions

We will now learn how to create our own functions

We will see that MATLAB functions follow very nicelythe steps of Top-Down Design

Define the function description text

Define the inputs and outputs function imprint

Define the algorithm that leads from input to output function body

Simple Custom Function

Functions are contained in M-files

The function name and file name should match

so the function distance should be in distance.m

For help about the distance function use

>> help distance

Now in matlab I can use it the same way as the built-in function

>> D=distance(0,0,10,10);

>> disp(D)

14.1060

function dist = distance(x1, y1, x2, y2)

%distance calculates the distance between two points (x1,y1) and (x2, y2)

dist = sqrt((x2-x1)^2+(y2-y1)^2);

end


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MATLAB Programs

Simple Custom Functions

function deg = degree2rad(x)

%degree2rad converts the input degree x into radians

deg=x*pi/180;

end

function rad = rad2degree(x)

%rad2degree converts the input radians x into degrees

rad=x*180/pi;

end

function f = fact(x)

%fact calculates the factorial of x

f=1;for i=1:x

f=f*i;

end

end

Custom Functions with more returnsfunction [large, small] = sort2(x,y)

%sort2 compares the two inputs and return them sorted, larger first.

if x>=y

large=x;

small=y;

else

large=y;

small=x;

end

end

>> [x,w]=sort2(5,10)

x =

10

w =

5

>> [x,w]=sort2(10,5)

x =

10

w =

5


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MATLAB Programs

Error Check Inputs

function x = correctInput(msg,low,high)

% correctInput prompt the user using msg for an input and

% error check to make sure it is >= low and > x=correctInput('enter num:',0,10);

enter num:-5

Error! enter num:11

Error! enter num:4>>

>> x

x =

4

Custom (User-Defined) Functions

function [out_arg1, out_arg2, ]

= fname(in_arg1, in_arg2, )

The word function is a keyword.

[out_arg1, out_arg2, ] is the output

argument list

fname is the name of the function

(in_arg1, in_arg2, ) is the input argumentlist

in_arg1, in_arg2, etc. are called dummy arguments

because they are filled will values when the function is

called


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MATLAB Programs

Script Vs. Function

Script

A script is executed line-

byline just as if you are

typing it into the Command

Window

The value of a variable in a

script is stored in the

Command Window

Workspace

Function

A function has its own

private (local) function

workspace that does not

interact with the workspace

of other functions or the

Command Window

workspace

Variables are not shared

between workspaces even ifthey have the same name

Local WorkpaceScript

w=5;

y=fact(w);

disp(y);

Function

function f = fact(x)

%fact calculates the factorial of x

f=1;

for n=1:x

f=f*n;

end

end

Command Window Workspace

contains w and y.

So f, x, and n are not known here

Function fact Workspace contains f, x, and n

When a function reaches the end of execution (and returns the output argument), the

function spacelocal spaceis deleted.


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MATLAB Programs

Persistent Variable

The variable count ispersistent

To clear it use>> clear functions

function func2

% func2 increments a persistent variable "count"

persistent count

if isempty(count)

count = 0;

end

count =count + 1;

fprintf('The value of count is %d\n',count);

end

>> func2

The value of count is 1

>> func2


>> func2


Use Functions for Clean and Organized

Code (Modular Programs)

x1=correctInput('Enter x1 from 0 to 10:',0,10);

y1=correctInput('Enter y1 from 0 to 10:',0,10);

x2=correctInput('Enter x2 from 0 to 10:',0,10);

y2=correctInput('Enter y2 from 0 to 10:',0,10);

d=distance(x1,y1,x2,y2);

fprintf('distance = %.2f\n',d);

m=correctInput('Enter math grade from 0 to 100:',0,100);

s=correctInput('Enter science grade from 0 to 100:',0,100);

e=correctInput('Enter englishgrade from 0 to 150:',0,150);

mr=grade2rank(m); % A function to convert grade numeric to alphanumeric

sr=grade2rank(s);

er=grade2rank(e);

fprintf('You got %s in math\n',mr);

fprintf('You got %s in science\n',sr);

fprintf('You got %s in english\n',er);

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06_GENN004m_MATLABPrograms