Introduction to matlab

INTRODUCTION TO MATLAB
PROGRAMMING
PRESENTED BY
DR. VIKRAM MUTNEJA,
ASSOCIATE PROFESSOR,
SHAHEED BHAGAT SINGH STATE
UNIVERSITY

WHAT IS MATLAB
 A product of MathWorks Incorporation, USA
 MathWorks is the leading developer of
mathematical computing software for engineers
and scientists.
 MATLAB is a platform, comprising of
 A programming Language
 An integrated development environment
 An interpreter based efficient execution engine

Brief History
 Cleve Moler, the chairman of the computer science department at the
University of New Mexico, started developing MATLAB in the late 1970s
 Recognizing its commercial potential, their team of trio (Cleve Moler, Jack
Little and Steve Bangert) rewrote MATLAB in C and founded MathWorks in
1984 to continue its development
 In 2000, MATLAB was rewritten to use a newer set of libraries for matrix
manipulation
 MATLAB was first adopted by researchers and practitioners in Control
Engineering, but later it quickly spread to many other domains
 It is now also used in education, in particular the teaching of linear algebra
and numerical analysis and very popular amongst scientists involved in the
field of Image Processing, Computer Vision, Artificial Intelligence, Robotics,
Mechatronics, Digital Signal processing, Parallel Computing and almost all
other domains of scientific computing

Why MATLAB
 It is a high level language cum platform
 Syntax is very simple
 It has a rich set of libraries and development
tools in the form of toolboxes and toolsets
 It is very easy to learn

MATRIX Laboratory
 All the variables/data objects declared in it are
in the form of MATRIX
 Even if the variable is single element, it will be
of type MATRIX i.e. of size 1 by 1 i.e. 1 row
and 1 column
 Case sensitive, i.e. a data object “a” will not be
same as “A”
 Rich set of statements for handling and
performing different operations on the data

Different sections of IDE
 Directory window: Shows the contents of existing
directory/folder
 Editor window: To display the editor
 Command window: Where commands can be
written and directly executed on MATLAB engine
 Workspace: Shows all the existing variables/data
objects
 History window: History of the commands
executed so far
 Current folder: To show/edit current working folder
also called as PWD i.e. Present Working Directory

Basic Commands to work in
command window
 clc
 Clear the screen
 close all
 To close all existing open windows
 clear all
 To clear all or particular existing variables/data objects i.e.
Its associated memory is freed
 PWD
 Present working directory
 dir
 To show the contents (files/folders) of the present working
directory in command window

Writing the program
 In the command window, type edit
 Editor will open
 Write your program and save in the current
folder with the desired name
 The extension of the MATLAB program file i.e.
Source code is .m

Compilation
 Unlike other high level languages e.g.
C++/Java, in MATLAB there is no need of
explicit compilation of your program
 MATLAB is an interpreter based platform, i.e.
Execution is done line by line in the MATLAB
engine
 So execution will be stopped at the point,
where ever it encounters error or until it has
finished executing the whole program
 We can demonstrate it with the help of an
example in MATLAB

Executing the Program
 Open the command window
 The name of the file to be executed should be
visible in the “current folder” section of
MATLAB IDE
 Type the name of the file without extension in
the command window
 File will be executed, and output displayed if
any
 Program can also be executed by “run” button
in the editor
 However to view if there is any output, you will
have to switch to command window

Using Variables
 Simple commands
 a=10
 b=‘Hello’;
 No need to explicitly declare the variables data
type
 It is by default considered by the compiler
based on the value assigned
 E.g. In above a will be considered as double
and b as character
 Double is the default numeric data type

Use of Semicolon
 What is use of semicolon at the end of the
statements in MATLAB? Is it part of syntax?
 Is it mandatory
 Answer: No
 It is used just to suppress displaying the output
of the statement
 i.e. If semicolon put then output is not
displayed, otherwise output (if any) will be
displayed

How to check all the existing data
objects along with their “class”
 By using the command “whos”
 In MATLAB, class means “data type”
 Sample output
Name Size Bytes Class Attributes
a 1x5 10 char
b 1x1 8 double
d 1x1 8 double

Printing the message or
variable
 Using the command “disp”
 disp(‘Hello MATLAB’)
 disp(a)
 Just by writing the name of the variable
(without semicolon) in command window
 Using the command “fprintf” (Equivalent of
printf statement of C Language)
 fprintf('The value of a = %dn',a);
 %d: class specifier, to display the double value
 n: Escape sequence for the new line

Taking input from user (Text
mode)
 Function to be used
 input
 Syntax
 Variable_name=input(‘Message String’,[‘s’]);
 Example (For numeric input)
 a=input(‘Enter the value of a’);
 Example (For character/string input)
 a=input(‘Enter the value of a’, ’s’);

Writing Loops
 For loop
 Syntax
for variable_name=index_start:[interval]:index_end
loop body..
.....
end
 Example
for i=1:2:30
disp(i)
end
Default value of interval is taken as unity

Writing Loops
 While loop
 Syntax
while(logical expression)
loop body..
.....
end
 Example
i=10;
while(i<30)
disp(i);
i=i+1;
end

Conditional Branching
 if instruction
 Syntax
If (logical expression)
....
end
 Example
a=input(‘Enter the value of a’);
If (a<10)
disp(‘value of a is less than 10’);
end

Conditional Branching (contd.)
 if-else instruction
 Syntax
If (logical expression)
....
else
....
end
 Example
If (a<10)
else
disp(‘value of a is greater than or equal to 10’);
end

Conditional Branching (contd.)
 if-elseif instruction (Multiple conditions to be checked)
 Syntax
If (expression1)
.......
elseif (expression2)
.......
elseif (expression3)
.......
.
.
else
........
end
 Example
If (a<10)
elseif(a==10)
disp(‘value of a is equal to 10’);
else
disp(‘value of a is greater than 0’);
end

Matrices and Arrays
 MATLAB is an abbreviation for "matrix
laboratory."
 While other programming languages mostly
work with numbers one at a time, MATLAB is
designed to operate primarily on whole
matrices and arrays
 "matrix" typically refers to a 2
dimensional array
 Whereas an "array" can be n-dimensional
 Any variable declared in MATLAB is by default
in the form of matrix only.

Array Creation
 a = [1 2 3 4]
This type of array is a row vector of size 1 by 4
 a = [1 2 3; 4 5 6; 7 8 10]
a = 3×3 Matrix
1 2 3
4 5 6
7 8 10
Note that semicolon has been used to initiate new
row

Array Creation (contd.)
 Another way to create a matrix is to use a function,
such as ones, zeros, or rand.
 For example, create a 5-by-1 column vector of zeros.
 z = zeros(5,1)
Output
z = 5×1
0
0
0
0
0

Array Creation (contd.)
 To create a matrix of random numbers
 Function used: magic
 Example
 A = magic(4)
 A = 4×4
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
 colon operator is used to create an equally spaced vector of values
using general form start:step:end
 Example
 B = 0:10:100
B = 1×11
0 10 20 30 40 50 60 70 80 90 100

Matrix and Array Operations
 MATLAB allows you to process all of the values in a matrix
using a single arithmetic operator or function.
a + 10
ans =
11 12 13
14 15 16
17 18 20
sin(a)
ans =
0.8415 0.9093 0.1411
-0.7568 -0.9589 -0.2794
0.6570 0.9894 -0.5440

Matrix and Array
Operations(Contd.)
 a = [1 2 3; 4 5 6; 7 8 10]
a =
1 2 3
4 5 6
7 8 10
To transpose a matrix, use a single quote (‘
a’
ans =
1 4 7
2 5 8
3 6 10

Matrix and Array
Operations(Contd.)
 Multiplication
 Multiplication is of two types
 Matrix multiplication
 Operator used is *
 E.g. A*B will multiply matrix A and B
 Element by element multiplication
 Operator used is .*
 E.g. A.*B will multiply matrix A and B, elementwise

Ways to Access Array
Elements
 Unlike other languages like C/C++ and JAVA in
which array indexing begins with 0, in MATLAB
it begins with 1
Description Example Description
Using specific row and
column
A(4,2) To access 2nd
element of 4th row
To use a single subscript
that traverses down each
column in order
A(8) Index converted to
linear value
columnwise
Accessing a range of rows
and columns
A(1:3,2) Elements of rows 1
to 3 and column 2
Accessing all the values in
particular dimension
A(3,:) Accessing all the
elements of row 3

Workspace Variables
 The workspace contains variables that you create within or
import into MATLAB from data files or other programs. For
example, these statements create variables A and B in the
workspace.
 A = magic(4); B = rand(3,5,2);
 You can view the contents of the workspace using command
whos
 Name Size Bytes Class Attributes
A 4x4 128 double
B 3x5x2 240 double
 The variables also appear in the Workspace pane on the
desktop

Saving Variables of
Workspace
 Workspace variables do not persist after you exit
MATLAB. Save your data for later use with
the save command as below
 save myfile.mat
 Note that extension of file has to “.mat”
 Restore data from a MAT-file into the workspace using load
 load myfile.mat
 Save command can be used to store particular variables too
as below:
 save(filename, variables)
 Example
 save test.mat X
Above command will save only the variable X to file test.mat

Loading data from Excel File
 Function to be used: xlsread
 Syntax
 Variable_name=xlsread(Name of excel file in single
quotes)
 Example
 num=xlsread(‘test1.xls’)
 Output (the contents of excel file loaded in workpace
variable “num”)
num =
10 11 12
11 12 14
12 13 16
13 14 18

 Another variant of xlsread
 Syntax
quotes, sheet)
 Example
 num=xlsread(‘test1.xls’,’sheet2’)
 Output (the contents of sheet2 of excel file loaded in
workpace variable “num”)
num =
10 11 12
24 12 11
38 13 10
52 14 9

 Syntax
quotes, sheet,range of cells in single quotes)
 Example
 num=xlsread(‘test1.xls’,’sheet2’,’B2:C4’)
 Output (the contents of cells in the range of B2 to B4 to
and C2 C4 of sheet2 of excel file loaded in workpace
variable “num”)
num =
12 11
13 10
14 9

Storing data to Excel File
 Function to be used: xlswrite
 Different variants of xlswrite
 xlswrite(filename,A)
 Writes the variable A to excel file, in first sheet (default)
 xlswrite(filename,A,sheet)
 Writes the variable A to excel file, in specified sheet
 xlswrite(filename,A,xlRange)
 Writes the variable A to excel file, in default sheet in given range of cells
 xlswrite(filename,A,sheet,xlRange)
 Writes the variable A to excel file, in specified sheet in given range of cells
 status = xlswrite(___)
 Returns the status=1 in case write is successful, and 0 in case of failure
 [status,message] = xlswrite(___)
 Additionally displays the message if generated by the write operation, which is loaded in
variable message
 Further advanced versions of xlsread and xlswrite are functions readtable
and writetable respectively.

Storing data to Excel File
 Syntax
quotes, sheet,range of cells in single quotes)
 Example
 num=xlsread(‘test1.xls’,’sheet2’,’B2:C4’)
 Output (the contents of cells in the range of B2 to B4 to
and C2 C4 of sheet2 of excel file loaded in workpace
variable “num”)
num =
12 11
13 10
14 9

Plotting
 Function to be used: plot
 Syntax
 Plot(X,Y): It will plot row vector Y versus row
vector X
 The length i.e. Number of elements of both vector
should be same
 Example
 X=[1 2 3 4 5 6] % Created a vector X
 Y=[2 2 3 4 7 9] % Created a vector Y
 plot(X,Y)

Plotting (Contd.)
 xlabel: to add the label to x-axis
 xlabel(‘label of the x axis’);
 ylabel: to add the label to y-axis
 ylabel(‘label of the y axis’);
 Title: to give title to the plot
 title(‘title of the plot’);
 Example
xlabel(‘X axis’);
ylabel(‘Y axis’);
Title(‘A demo Plot’);

Plotting (contd.)
 Combining multiple line plots into single plot,
single figure
 plot(X1,Y1,...,Xn,Yn)
 Example code
x = linspace(-2*pi,2*pi);
y1 = sin(x);
y2 = cos(x);
figure
plot(x,y1,x,y2)

Plotting (contd.)
 Create Line Plot From Matrix
 Example code
%Creating a 4 by 4 matrix of random numbers
Y = magic(4)
%Creating the new figure
figure
%Plotting the columns of Y
plot(Y)
 Plots each matrix column as a separate line

Plotting (contd.)
 Combing multiple plots in single figure
using subplot
 Syntax: subplot(NR,NC,Position number)
 Where
 NR: Number of Columns in figure
 NC: Number of Columns in figure
 Position: Position where this plot has to be shown

Plotting (contd.)
 Sample Output

That is all for now...
 Thanks
 Any Queries Please

Introduction to matlab

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