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Programming in MATLAB

ELEC 206Computer Applications for

Electrical Engineers

Dr. Ron Hayne

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Problems with Two Variables

Two Scalars

x = 3;

y = 5;

A = x * y

A = 15

Scalar and Vector

x = 1:5;

y = 5;

A = x * y A = 5 10 15 20 25

Two Vectors

x = 1:5;

y = 1:0.5:3;

A = x * y

Error

Two Vectors (by element)

x = 1:5;

y = 1:0.5:3;

A = x .* y A = 1 3 6 10 15

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Results of element-by-element calculations

All combinations of x and y

[X Y] = meshgrid(x,y)

A = X .* Y

x

1 2 3 4 5

1.0 1

1.5 3

y 2.0 6

2.5 10

3.0 ? 15

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Example

Plot voltage vs time for various RC time constants

/

0

t e

V

v

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Voltage vs Time for Various Time Constants

Time

V o l t a g e

tau=0.5

tau=1.0

tau=2.0

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Example

time = 0:0.1:5;

tau = [0.5 1.0 2.0]; [TIME TAU] = meshgrid(time,tau);

V = exp(-TIME./TAU);

plot(time,V)

/

0

t e

V

v

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Input / Output

User Defined Input

Prompt user for input

var = input('Prompt string')

Output Options Display Function

disp(var)

disp('Output string')

Number to String Function num2str(var)

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Input / Output

Formatted Output

fprintf('format string', var, ...)

%f fixed point

%e exponential notation

%w.pf w=width, p=precision

\n linefeed (endl)

\t tab

Example

fprintf('The answer is %5.2f volts.\n', v)

The answer is 5.25 volts.

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Input / Output

Formatted Output

Example

patient = 1:3;

temp = [98.6, 100.1, 99.2];

hist = [patient;temp];

fprintf('Patient %3.0f temp of %6.1f\n',hist)

Patient 1 temp of 98.6



2.991.1006.98

0.30.20.1

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Example Revisited

% RC Time Constant Example with User Input clear, clc % Request input from user v0 = input('Input initial voltage: '); tau = input('Input 3 time constants as a vector: '); last = input('Input max time: '); incr = input('Input time increment: '); time = 0:incr:last; [TIME TAU] = meshgrid(time,tau);

V = v0*exp(-TIME./TAU); plot(time,V) legend(num2str(tau(1)),num2str(tau(2)),...

num2str(tau(3)))

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Functions

Functions written as M-files

function s=add3(x)

% Function that adds 3 to array x

s=x+3;

File name must be same as function name add3.m

Comments used by help function

help add3

Used like built-in MATLAB functions x=[1 2 3];

add3(x)

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Functions

Functions with multiple outputs

function [dist vel accel]=motion(t)

% Function to calculate distance, velocity and acceleration

accel = 0.5 * t; vel = accel .* t;

dist = vel .* t;

Local variables not visible outside function

function s=add3(x) % Function that adds 3 to array x

a=x+3;

s=a;

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Example

Degrees / Radians Conversion Functions

Problem Statement

Create and test two functions:

DR to change from degrees to radians RD to change from radians to degrees

Input/Output Description

Table of degrees to radians Vector of degree values

Table of radians to degreesVector of radian values

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Example

Hand Example

degrees = radians * 180/pi

radians = degrees * pi/180

Algorithm Development Define vector of degree values

Call DR function to find radians

Output results in a table

Define vector of radian values

Call RD function to find degrees

Output results in a table

Degrees Radians

0 0

30 0.524

60 1.04790 1.571

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MATLAB Solution

Functions

function output=DR(x) %This function changes degrees to radians

output=x*pi/180;

function output=RD(x) %This function changes radians to degrees

output=x*180/pi;

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MATLAB Solution

%Example 5.4 clear, clc %Define a vector of degree values degrees = 0:15:180; % Call the DR function, and use it to find radians radians = DR(degrees); %Create a table to use in the output degrees_radians =[degrees;radians]; %Generate an output table disp('A table of degrees to radians') disp('degrees radians') fprintf('%6.0f %8.3f\n',degrees_radians) %Put a blank line in output to separate tables disp(' ')

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MATLAB Solution

%Define a vector of radian values radians = 0:pi/12:pi; %Call the RD function, and use it to find degrees degrees = RD(radians); %Generate an output table disp('A table of radians to degrees') disp('radians degrees') fprintf('%9.3f %10.3f \n',[radians;degrees])

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Control Structures

Sequence

Sequence of steps performed one after another

Selection

Condition evaluated as true or false if true, one set of statements executed

if false, another set of statements executed

Repetition

Repeat (loop through) a set of steps

As long as a condition is true

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Conditional Expressions

Relational Operators

< less than

<= less than or equal to

> greater than >= greater than or equal to

== equal to

~= not equal

True and False 1 True

0 False

Logical Operators

& and

| or

~ not

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Selection Structures

find Command

Often used instead of both if and loop structures

Returns vector of indices of nonzero elements of vector

Example temp = [100 98 94 101 92];

faulty = find(temp<95);

failtable = [faulty' temp(faulty)']

Example with 2D Matrix...

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Selection Structures

if Statement

if condition

statements

end if/else Statement

if condition

statements

else

statements

end

if/elseif/else Statement

if condition

statements

elseif conditionstatements

else

statements

end

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Example

Assign Letter Grades Scalar Functionfunction g = grade(x) %This function requires a scalar input if(x>=90)

g = 'A'; elseif(x>=80)

g = 'B'; elseif(x>=70)

g = 'C';

elseif(x>=60) g = 'D';

else g = 'F';

end

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Example Revisited

Assign Letter Grades Vector Functionfunction g = gradev(x) % This function works with vector input

A = find(x>=90); B = find(x>=80 & x<90); C = find(x>=70 & x<80); D = find(x>=60 & x<70); F = find(x<60); g(A) = 'A';

g(B) = 'B'; g(C) = 'C'; g(D) = 'D'; g(F) = 'F';

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Loops

Usually not necessary in MATLAB

Avoid the temptation

Much slower

Use matrix calculations and find instead

For Loops for index=expression

statements

end

While Loops while condition

statements

end

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Loop Example

For Loop

A=ones(200);

for k=1:length(A(:))

B(k)=A(k)*pi;end

Matrix Operation

A=ones(200);

B=A*pi;

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Summary


Input / Output

Functions

Control Structures

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