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Introduction to Matlab
Original: Jing Wang
Presenter: Abdul Jabbar Siddiqui
Date: January 20th, 2017
What is Matlab
• High level language for technical computing
• Stands for MATrix LABoratory
• Everything is a matrix - easy to do linear algebra
• MATLAB is available for Windows, Macintosh and
UNIX systems. It is used by more than one million
people in industry and academia.
The basics
2
The basics:
Matrix calculation
•
^: exponentiation
•
*: multiplication
•
/: division
•
+: addition
•
-: subtraction
Array Operations
• Evaluated element by element
.' : array transpose
.^ : array power
.* : array multiplication
./ : array division
>> A=[1 2;3 4];
>> B=[5 6;7 8];
>> A*B
19
22
43
50
But:
>> A=[1 2;3 4];
>> A^2
7
10
15
22
But:
>> A.*B
5
21
>> A.^2
1
9
12
32
4
16
Some Built-in functions
• mean(A):mean value of a vector
• max(A), min (A): maximum and minimum.
• sum(A): summation.
• median(A): median value
• std(A): standard deviation.
• det(A) : determinant of a square matrix
• Inv(A): Inverse of a matrix A
Indexing Matrices
Given the matrix: A
m
Then:
n
=
0.9501
0.2311
0.6068
0.4860
0.4231
0.2774
A(1,2) = 0.6068
Aij ,i = 1...m, j = 1...n
A(3) = 0.6068
index = (i −1)m + j
A(:,1) = [0.9501
1:m
0.2311 ]
A(1,2:3)=[0.6068
0.4231]
Adding Elements to a Vector or a Matrix
>> A=1:3
A=
1 2 3
>> A(4:6)=5:2:9
A=
1 2 3 5 7
>> B=1:2
B=
1 2
>> B(5)=7;
B=
1 2 0
0
7
9
>> C=[1 2; 3 4]
C=
1 2
3 4
>> C(3,:)=[5 6];
C=
1 2
3 4
5 6
>> D=linspace(4,12,3);
>> E=[C D’]
E=
1 2 4
3 4 8
5 6 12
Graphics - 2D Plots
plot(xdata, ydata, ‘marker_style’);
For example:
>> x=-5:0.1:5;
>> sqr=x.^2;
>> pl1=plot(x, sqr, 'r:o');
Graphics - Overlay Plots
Use
hold on for overlaying graphs
So the following:
Gives:
>> hold on;
>> cub=x.^3;
>> pl2=plot(x, cub,‘b:s');
Graphics - Annotation
Use title,
annotation
xlabel, ylabel and legend for
>> title('Demo plot');
>> xlabel('X Axis');
>> ylabel('Y Axis');
>> legend([pl1, pl2], 'x^2', 'x^3');
Graphics-Stem()
• stem()is to plot discrete sequence data
• The usage of stem() is very similar to plot()
cos(nπ/4)
1
>>
>>
>>
>>
n=-10:10;
f=stem(n,cos(n*pi/4))
title('cos(n\pi/4)')
xlabel('n')
0.5
0
-0.5
-1
-10
-5
0
n
5
10
subplots
• Use subplots to divide a plotting window into several
panes. Create a .m script.
x=0:0.1:10;
f=figure;
f1=subplot(1,2,1);
plot(x,cos(x),'r');
grid on;
title('Cosine')
f2=subplot(1,2,2);
plot(x,sin(x),'d');
grid on;
title('Sine');
Cos ine
S ine
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
-0.2
-0.2
-0.4
-0.4
-0.6
-0.6
-0.8
-0.8
-1
0
5
10
-1
0
5
10
Audio signal command
waveplay(y,Fs);
• Plays the audio signal stored in the vector y on a PCbased audio output device. You specify the audio signal
sampling rate with the integer Fs in samples per
second. The default value for Fs is 11025Hz.
• .wave file is a file format for storing the signal
amplitude of a sound wave. It can be
loaded into MATLAB, displayed, processed, played, and
written back to a disk file
Audio signal command
[y, Fs, bits] = wavread(‘tarzan.wav’);
• - y is a vector containing the signal amplitude in ‘tarzan.wav’
- Fs is a scalar representing the sampling frequency
- bits is a scalar representing the sampling depth
(e.g. 8 bits used to represent one sample)
wavwrite(y,Fs,N,filename)
• - writes the data stored in the variable y to a WAVE file
called filename. The data
has a sample rate of Fs Hz and is N-bit.
Discrete Fourier Transform
Discrete Fourier Transform
M-files : Script and function files
When problems become complicated and require re–
evaluation, entering command at MATLAB prompt is
not practical
Solution : use M-files
Script
Function
Collections of commands
User defined commands
Executed in sequence when called
Normally has input &
output
Saved with extension “.m”
Saved with extension “.m”
M-files : script and function files (function)
• Function is a ‘black box’ that communicates with
workspace through input and output variables.
INPUT
FUNCTION
– Commands
– Functions
– Intermediate variables
OUTPUT
M-files : script and function files (function)
Every function must begin with a header:
function output=function_name(inputs)
Output variable
Must match the
file name
input variable
function y=add3(a)
a=a+1;
a=a+1;
y=a+1;
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Debugging with Matlab
•
Examine/change the value
of variables
•
Look at the stack of
function
•
Evaluate arbitrary
expression
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Flow Control：(if, while , for)
• If Statement Syntax
if (Condition_1)
Matlab Commands
elseif (Condition_2)
Matlab Commands
elseif (Condition_3)
Matlab Commands
else
Matlab Commands
end
Some Dummy Examples
if ((a>3) & (b==5))
Some Matlab Commands;
end
if (a<3)
Some Matlab Commands;
elseif (b~=5)
Some Matlab Commands;
end
if (a<3)
Some Matlab Commands;
else
Some Matlab Commands;
end
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• While Loop Syntax
while (condition)
Matlab Commands
end
Dummy Example
while ((a>3) & (b==5))
Some Matlab Commands;
end
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Some Dummy Examples
• For loop syntax
for i=Index_Array
Matlab Commands
end
for i=1:100
Some Matlab Commands;
end
for j=1:3:200
Some Matlab Commands;
end
for m=13:-0.2:-21
Some Matlab Commands;
end
for k=[0.1 0.3 -13 12 7 -9.3]
Some Matlab Commands;
end
Practice Problems
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Time domain Signal plot
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Practice Problems
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Frequency spectrum
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