In this article, we are giving an
introduction to MATLAB. This article is part of a tutorial series we are
developing for MATLAB. We hope you to give us feedback, so that we can
improve our MATLAB tutorial series.
What does MATLAB stand for?
MATLAB stands for MATrix LABoratory.
Hence, as the name suggests, here you play around with matrices. Using
MATLAB an image (or any other data like sound, etc.) can be converted
to a matrix and then various operations can be performed on it to get
the desired results and values. Image processing is quite a vast field
to deal with. We can identify colors, intensity, edges, texture or
pattern in an image. In this tutorial, we would be restricting ourselves
to detecting colours (using RGB values) only.
Getting acquainted with MATLAB environment
For those who have just finished
installing MATLAB on their system and can’t figure out from where to
start, no need to worry! This tutorial will first make you well
acquainted with its very basics and then move further.
So, a typical MATLAB 2009 window looks like the image shown below.
As marked in the image, there are 4 main windows.
Command window:
This is the main window where you write the commands, as well as see
the outputs. In other words, here is your interaction with the software.
Command History:
As the name suggests, it shows the list of the commands recently used
in chronological order. Hence, you can double click on a command to
execute it again.
Current directory:
It is the default directory (folder) for saving your files. All the
files which you make (like mfiles, as discussed later) are saved here
and can be accessed from here directly. The location of the current
directory is shown in the toolbar at the top. You can change it by
changing the address here.
Workspace: It displays the list of the variables defined by you in the current session of MATLAB.
The Menu bar and Toolbar: The
toolbar has buttons for common operations like cut, copy,
paste, undo, redo. The most important button here is the HELP
button. It opens the MATLAB help window which looks as the screenshot
given below.
You
can get the details of any MATLAB command/function here and
many demos of some commonly used applications. Locate the four tabs:
Contents, Index, Search Results and Demos on the left. One of the best
ways to learn by yourself is to look for demos of your interest and type
the command/ function which you encounter there as the search term. You
will then get the complete details of the function like its use,
syntax, as well as few examples on how to use it. You can also have a
look at some of the related functions at the end of page under the
heading “See Also”. The demos related to Image Processing can be found
under Image Processing Toolbox and Image Acquisition Toolbox.
Now once we are done with knowing the
essential features of MATLAB, let’s start typing something in the
command window, say: a=5 and press enter.
Yes… as you can see that MATLAB creates a variable with name ‘a’, stores value 5 in it and displays it in the command window itself. Hence you can see how userfriendly MATLAB is.
Variables are stored in the form of Matrices in MATLAB. Hence, ‘a’ is a 1X1 matrix in the above example. Similarly, you can make one dimensional, two dimensional, etc. matrices as follows:
>> a=[1 3 5 7 9]To avoid the display of the variable, we use semicolon (;) at the end of instruction.
a =
1 3 5 7 9
>> b=[1 2 3;4 5 6;7 8 9]
b =
1 2 3
4 5 6
7 8 9
>> b=[1 2 3;4 5 6;7 8 9];The indices of matrices in MATLAB start from 1 (unlike C/C++ and Java where they start from 0). We refer to a particular element of the matrix by giving its indices in parenthesis ().
>> b(2,1)Now with the variables in hand, you can perform various mathematical operations on them directly.
ans =4
>> a=[1 2 3];ans is the default variable of MATLAB. You can also store the result in another variable as
>> b=[6 7 8];
>> a+b
ans =
7 9 11
>> c=a+b c =
7 9 11
General functions & commands in MATLAB
clc: To clear the command window, giving you a ‘clear screen’.clear: To remove all variables from the workspace. This frees up system memory.
Trigonometric functions
For angle in radians>> sin(1)For angle in degrees
ans =0.8415
>> sind(30)Inverse trigonometric
ans =0.5000
>> asin(1)Similarly we have cos(), cosd(), acos(), tan() and other functions.
ans =1.5708
>> asind(.5)
ans =30.0000
The Colon Operator
The colon is one of the most useful
operators in MATLAB. It can create vectors, subscript arrays, and
specify for iterations. In a very crude language, we can say
that the colon (:) means “throughout the range”.
j:k is the same as [j,j+1,...,k]Example:
j:i:k is the same as [j,j+i,j+2i, ...,k] A(:,j) is the jth column of A
A(:,j:k) is A(:,j), A(:,j+1),…,A(:,k)
A(:) is all the elements of A, regarded as a single column.
>> a= [1 2 3; 4 5 6; 7 8 9]
a =
1 2 3
4 5 6
7 8 9
>> a(:,2:3)
ans =
2 3
5 6
8 9
Relational Operators
Operator  Description 
==

Equal to 
~=

Not equal to 
<

Less than 
<=

Less than or equal to 
>

More than 
>=

More than or equal to 
Frequently used Functions & Commands
Conditional Statements
if, else: Execute statements if condition is true, false respectively.Syntax:
if condition1 statementExample:
elseif condition 2 statement
else
statement end
a=10;*Note: As a block is contained in braces {} in C/C++/Java, a block is terminated by the ‘end’statement in MATLAB.
>> if a<10 b=a/2;
else
b=a*2;
end
>> b
b =20
LOOPing Commands
for: To create a loop – that is to execute a block of code specified number of times.Syntax:
for variable = initval:endval statementExample
… statement
end
>>c=[1 2 3 4 5]; b=0;while: Again to create loop, that executes till a specified condition is true.
>>for i=1:5 b=b+c(i); end
>> b
b =15
Syntax:
while condition statementsExample:
end
>> c=2009; i=1; while c>1 b(i)=mod(c,10); c=c/10; i=i+1; endzeros(): Create array/matrix of all zeros.
>> b
b =9.0000 0.9000 0.0900 2.0090
B = zeros(n) returns an nbyn matrix of zeros.
B = zeros(m,n) returns an mbyn matrix of zeros. Example,
>> z=zeros(2,4)Similarly we have ones() function for all values 1.
z =
0 0 00 0 0 00
size(): Returns matrix dimensions.
Example:
for the above matrix z,
>> size(z)length(): Returns the length of a vector. For an array, it returns the size of the longest dimension.
ans =
2 4
Example:
>>x = ones(1,8);dot(): Returns dot product of two vectors.
>>n = length(x)
n =8
Example:
C = dot(A,B)sqrt(): Returns square root of each element of an array
min(): Returns smallest elements in an array.
Syntax:
C = min(A)If A is a matrix, min(A) treats the columns of A as vectors, returning a row vector containing the minimum element from each column. Similarly we have max() function.
sort(): Sorts array elements in ascending or descending order
Syntax:
B=sort(A,mode)where value of mode can be
‘ascend’ : Ascending order (default)plot(): Creates a 2D line plot
‘descend’ : Descending order
So these all are the frequently used
functions/commands in MATLAB. Until we come with our next chapter in
MATLAB tutorial series, please share this article with your friends.
Give us your feedback on improving the tutorial as well, we value it!
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