Transcript Programming in MATLAB

Programming in MATLAB
ELEC 206
Computer Applications for
Electrical Engineers
Dr. Ron Hayne
Problems with Two Variables
 Two Scalars
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x
y
A
A
=
=
=
=
 Two Vectors
3;
5;
x * y
15
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 Scalar and Vector
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x
y
A
A
=
=
=
=
x = 1:5;
y = 1:0.5:3;
A = x * y
Error
 Two Vectors (by element)
1:5;
5;
x * y
5 10 15 20 25
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x
y
A
A
=
=
=
=
1:5;
1:0.5:3;
x .* y
1 3 6 10 15
2
Problems with Two Variables
 Results of element-by-element calculations
x
1
1.0
1.5
y
2.0
2
3
5
1
3
6
2.5
3.0
4
10
?
15
 All combinations of x and y
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[X Y] = meshgrid(x,y)
A = X .* Y
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Example
 Plot voltage vs time for various RC time constants
v
 e t / 
V0
Voltage vs Time for Various Time Constants
1
tau=0.5
tau=1.0
tau=2.0
0.9
0.8
0.7
Voltage
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.5
1
1.5
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2.5
Time
3
3.5
4
4.5
5
4
Example
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v
 e t / 
V0
time = 0:0.1:5;
tau = [0.5 1.0 2.0];
[TIME TAU] = meshgrid(time,tau);
V = exp(-TIME./TAU);
plot(time,V)
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Input / Output
 User Defined Input
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Prompt user for input
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var = input('Prompt string')
 Output Options
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Display Function
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disp(var)
disp('Output string')
Number to String Function
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num2str(var)
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Input / Output
 Formatted Output
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fprintf('format string', var, ...)
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%f
%e
%w.pf
\n
\t
fixed point
exponential notation
w=width, p=precision
linefeed (endl)
tab
Example
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fprintf('The answer is %5.2f volts.\n', v)
The answer is
5.25 volts.
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Input / Output
 Formatted Output
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Example
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patient = 1:3;
temp = [98.6, 100.1, 99.2];
hist = [patient;temp];
2.0
3.0 
 1.0
98.6 100.1 99.2


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fprintf('Patient %3.0f temp of %6.1f\n',hist)
Patient
Patient
Patient
1 temp of
2 temp of
3 temp of
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98.6
100.1
99.2
8
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
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function s=add3(x)
% Function that adds 3 to array x
s=x+3;
 File name must be same as function name
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add3.m
 Comments used by help function
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help add3
 Used like built-in MATLAB functions
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x=[1 2 3];
add3(x)
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Functions
 Functions with multiple outputs
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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
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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
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Problem Statement
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Create and test two functions:
 DR to change from degrees to radians
 RD to change from radians to degrees
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Input/Output Description
Vector of degree values
Table of degrees to radians
Vector of radian values
Table of radians to degrees
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Example
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Hand Example
Degrees Radians
degrees = radians * 180/pi
 radians = degrees * pi/180
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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
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0
30
60
90
0
0.524
1.047
1.571
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MATLAB Solution
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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
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Sequence of steps performed one after another
 Selection
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Condition evaluated as true or false
if true, one set of statements executed
if false, another set of statements executed
 Repetition
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Repeat (loop through) a set of steps
As long as a condition is true
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Conditional Expressions
 Relational Operators
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<
<=
>
>=
==
~=
 Logical Operators
less than
less than or equal to
greater than
greater than or equal to
equal to
not equal
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&
|
~
and
or
not
 True and False
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1
0
True
False
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Selection Structures
 find Command
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Often used instead of both if and loop structures
Returns vector of indices of nonzero elements of vector
 Example
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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/elseif/else Statement
if condition
statements
end
if condition
statements
elseif condition
statements
else
statements
end
 if/else Statement
if condition
statements
else
statements
end
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Example
 Assign Letter Grades Scalar Function
function 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 Function
function 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
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Avoid the temptation
 Much slower
Use matrix calculations and find instead
 For Loops
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for index=expression
statements
end
 While Loops
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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
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Problems with Two Variables
Input / Output
Functions
Control Structures
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