Introduction to MATLAB
The language of Technical Computing
MATLAB
MATrix LABoratory- Everything is
represented by matrices!
 It is a program for doing Numerical
Computation.
 Also used widely as a programming
language to develop tools for Machine
Learning.

Why MATLAB?
Large toolbox of numeric/image library
functions.
 Very useful for displaying, visualizing data.
 High-level: focus on algorithm structure,
not on low-level details.
 allows quick prototype development of
algorithms.
 It is an Interpreter, not as fast as
compiled code.

The MATLAB Environment
Variables
MATLAB treats all variables as matrices.
For our purposes a matrix can be thought
of as an array, in fact, that is how it is
stored.
 Vectors are special forms of matrices and
contain only one row OR one column.
 Scalars are matrices with only one row
AND one column.

MATLAB Programming
The symbol “%” is used to indicate a
Comment.
 A “;” at the end of the line implies
MATLAB won’t print the output of the
statement. Otherwise it will print the
output, which is sometimes useful for
printing variable values.

MATLAB Programming
a = [1,2,3,4]
MATLAB Output:
a=
1 2 3 4

a=[1,2,3,4]; %Notice the semicolon
MATLAB Output:
<Empty>

Command Line
MATLAB's command line is like a
standard shell:
- Up arrow to recall commands without
retyping and down arrow to go forward.
 Opening a new file in editor:
>> edit test.m
 MATLAB source file extension is .m.
 Running a program : >> test

MATLAB Programming
a = [1 2; 3 4]; % Creates a 2x2 matrix
 The simplest way to create a matrix is to
list its entries in square brackets. The ";"
symbol separates rows; the (optional) ","
separates columns.
 N = 5 % A scalar
 v = [1 0 0] % A row vector

MATLAB Programming
v = [1; 2; 3] % A column vector
 v = v’
Transpose a Vector or Matrix(row to
column and column to row)
 v = []
Empty Vector

MATLAB Programming
m = zeros(2, 3)
Creates a 2x3 matrix of zeros
 v = ones(1, 3)
Creates a 1x3 matrix (row vector) of ones
 m = eye(3) %Identity matrix (3x3)
 v = rand(3, 1)
Randomly filled
3x1 matrix (column vector)

Indexing in MATLAB
 REMEBER: Indices always start from
“1”, not “0”.
 Matrix(ROW#,COLUMN#)
 m(1,3) %1st row 3rd column
 m(2,:) %access whole second row
 m(:,3) %access whole second column
Operators
Assignment = a = b (assign b to a)
 Addition + a + b
 Subtraction - a -b
 Multiplication * or .* a*b or a.*b
 Division / or ./ a/b or a./b
 Power ^ or .^ a^b or a.^b
 A “.” means element wise operation

Conditional Structures
for i=1:2:7 %Loop from 1 to 7, steps of 2
if(i==3)
disp(‘i is 3’) %print output
elseif(i==5)
disp(‘i is 5’)
end
end
Functions
All functions are separate m-files.
 The first line in a function file must be of
this form:
function [outarg_1, ..., outarg_m] =
myfunction(inarg_1, ..., inarg_n)
 The function name should be the same as
that of the file.

Function Example

myfunction.m
function y = myfunction(x)
a = [-2 -1 0 1];
y = a + x;
Function Example

anotherfunction.m
function [y, z] = anotherfunction(a, b)
y = a + b;
z = a - b;
Plotting
x=rand(1,100);
y=rand(1,100);
plot(x,y,’*’);
Plotting
To put a label on X-Axis
xlabel(‘my x label’);

To put a label on Y-Axis
ylabel(‘my y label’);

To put a Title of the Plot
title(‘my title’);

MATLAB Image Processing
Image Processing Toolbox is needed.
 I=imread(‘cute_baby.jpg’); %read Image
imshow(I) %show image

MATLAB Image Processing
I2=rgb2gray(I); % convert RGB to gray
imwrite(I2, ‘cute.jpg’); % save gray image
figure, imshow(I2) % image in new figure
MATLAB Image Processing
figure,imhist(I2) % show histogram
MATLAB Image Processing

From the histogram, we see that the
image intensity is missing low values, only
high values are present.
MATLAB Image Processing
I3 = histeq(I2); %Histogram Equalization
figure, imhist(I3);
MATLAB Image Processing
figure, imshow(I2) %Original image
figure, imshow(I3) % Equalized Image
Help with MATLAB
Type help at the MATLAB prompt or
help followed by a function name for help
on a specific function.
 Online documentation for MATLAB at
the MathWorks website:
www.mathworks.com
 There are also numerous tutorials online
that are easily found with a web search.
