Basics of programming in matlab

SESSION-1

INTRODUCTION TO
PROGRAMMING IN MATLAB
LANGUAGE

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Programming Basics
 To Start Matlab
 On Microsoft® Windows® platforms,
double-clicking the MATLAB shortcut on your
Windows desktop.

Matlab.ico
 On UNIX platforms, start MATLAB by typing matlab at
the operating system prompt.
Quitting the MATLAB Program
 To end your MATLAB session, select File > Exit
MATLAB in the desktop, or type quit in the Command
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Programming in Matlab

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Basics of Matlab
 Matlab has two different methods for executing commands

Interactive mode
In interactive mode, commands are typed (or cut-and-pasted) into the
'command window'.
 »3+ 4
 ans =
 7

 Batch mode.
In batch mode, a series of commands are saved in a text file (either
using Matlab's built-in editor, or another text editor ) with a '.m'
extension.
The batch commands in a file are then executed by typing the name of
the file at the Matlab command prompt.

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Scripts and Functions
M-Files:
Files that contain code in the MATLAB language
are called M-files. You create M-files using a text
editor, then use them as you would any other
MATLAB function or command.
 There are two kinds of M-files:

1. Scripts, which do not accept input arguments or
return output arguments. They operate on data in
the workspace.
2. Functions, which can accept input arguments and
return output arguments. Internal variables are
local to the function.
NOTE :The names of the M-file and of the function
should be the same.
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Example
Scripts
 x = -pi:0.01:pi;
 plot(x,sin(x)), grid on

Function
 %Name of function is sum1
 function c=sum1(a,b)
 c=a+b
 end
 M file names should be sum1.m

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Variables
 As in programming languages, the MATLAB language provides
mathematical expressions, but unlike most programming
languages, these expressions involve entire matrices.
 MATLAB does not require any type declarations or dimension
statements. When MATLAB encounters a new variable name, it
automatically creates the variable and allocates the appropriate
amount of storage. If the variable already exists, MATLAB changes
its contents and, if necessary, allocates new storage. For example,
 num_students = 25 creates a 1-by-1 matrix named num_students
and stores the value 25 in its single element.
To view the matrix assigned to any variable, simply enter the
variable name.
 Variable names consist of a letter, followed by any number of
letters, digits, or underscores.(max length of variable is 63)
 MATLAB is case sensitive; it distinguishes between uppercase and
lowercase letters. B and b are not the same variable.

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MATLAB AND MATRIX

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MATRIX
*MATLAB IS MATRIX MANIPULATION LANGUAGE.
*MOST OF VARIABLES YOU DECLARE WILL BE
MATRICES.
*MATRIX IS RECTANGULAR ARRAY OF NUMBERS
*A is MxN MATRIX : IT MEANS ‘A’ HAS M ROWS AND N
COLUMNS
*IN MATRIX FIRST INDEX IS ROW INDEX AND SECOND
INDEX IS COLUMN INDEX
*SCALAR IS 1x1 MATRIX.
*INDEXING IN MATLAB STARTS FROM ONE(1)
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DEFINING MATRIX IN MATLAB
Let matrix
B=
1 2 3
6 7 8
B CAN BE CREATE IN MATLAB USING SYNTAX
B=[1 2 3;6 7 8];
HOW TO ACCESS DIFFERENT ELEMENTS B(ROW ,COLUMN)
B(1,1)=1 i.e. FIRST ROW and FIRST COLUMN
B(2,1)=6 i.e. SECOND ROW FIRST COLUMN
B(2,3)=8 i.e. SECOND ROW THIRD COLUMN
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ACCESSING SUBMATRICES
A=
11 12 13 14 15 16
17 18 19 20 21 22
23 24 25 26 27 28
A(1,:) = [11 12 13 14 15 16]
i.e. FIRST ROW AND ALL COLUMNS
A(2,:)=[17 18 19 20 21 22]
i.e. SECOND ROW AND ALL COLUMNS
A(1,1:3)=[11 12 13 ];
i.e. FIRST ROW AND ONE TO THREE COLUMNS
A(2,3:6)=[19 20 21 22 ]; i.e second row , third to sixth column.
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ONE DIMENTION MATRIX

ONE DIMENTION MATRIX IS ALSO KNOWN AS VECTOR.
ONE DIMENTION MATRIX MAY BE EITHER
ROW MATRIX : CONTAINING ONE ROW ONLY
OR
COLUMN MATRIX:CONTAINING ONE COLUMN ONLY
HOW TO ACCES DIFFERENT ELEMENTS
A(1),A(2) WILL WORK AS IT IS ONE DIMENSIONAL VECTOR.

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ALTERNATE WAY OF MAKING MATRICES

A=1:9
A=
1 2 3 4 5 6 7 8 9
A=1:2:9
A=
1 3 5 7 9
A=[5:-1:-5]
A=
5 4 3 2 1 0 -1 -2 -3 -4 -5
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MATRIX BUILDING FUNCTIONS

eyes(n) will produce nxn identity matrix
eyes(m,n) will produce mxn identity matrix
ones(n) will produce nxn matrix of ones.
ones(m,n) will produce mxn matrix of ones.
zeros(m,n) will produce matrix of zeros
rand(m,n) will produce mxn matrix of randomvalue
triu(X) will extract upper triangular part of matrix X.
tril(X) will extract lower triangular part of matrix X.

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MATRIX OPERATIONS

+ ADDITION
- SUBTRACTION
* MULTIPLICATION
^ POWER
‘ CONJUGATE TRANSPOSE
.’ TRANSPOSE
LEFT DIVISION
/ RIGHT DIVISION

THESE MATRIX OPERATIONS APPLY TO SCALARS AS WELL.
IF THE SIZES OF MATRICES ARE INCOMPATIBLE FOR THE
MATRIX OPERATION, AN ERROR MESSAGE WILL RESULT.

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EXAMPLE OF MULTIPLICATION
A= B=
1 2 1 1
2 3 1 1

A*B
1*1+2*1 1*1+2*1
2*1+3*1 2*1+3*1
A*B
3 3
5 5

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ENTRY-WISE OPERATIONS
•OPERATIONS OF ADDITION AND SUBTRACTION ALREADY
OPERATE ENTRY WISE
A= B=

1 2 1 1
2 1 1 1

A+B

2 3
3 2

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Other entry-wise operation

i.e. .* , .^ , ./ ,.
A=[1 2 3 4]
B=[1 2 3 4]

A.*B=[1 4 9 16]
A=[4 6 8 10]
B=[2 2 2 2]

A./B=[2 3 4 5]
A=[1 2 3]
A.^3=[1 8 27]
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MATRIX DIVISION
IF A IS AN INVERTIBLE MATRIX AND b IS A COMPATIBLE
COLUMN VECTOR, then
x=Ab is the solution of A*x=b
[1 2 3;4 5 6; 8 9 7]*[x;y;z]=[1;2;3]
[x;y;z]=[1 2 3;4 5 6;8 9 7][1;2;3]

IF A IS AN INVERTIBLE MATRIX AND b IS A COMPATIBLE
ROW VECTOR, then
x=b/A is the solution of x*A=b
[x y z]*[1 2 3;4 5 6; 8 9 7]=[1 1 3]
[x y z]=[1 1 3]/[1 2 3;4 5 6;8 9 7]
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STATEMENTS, EXPRESIONS AND
VARIABLES

•MATLAB is interpreted language.
•Statements are of form
variable=expression;
expression;
x=3;
y=x^3+3*x;
y=sqrt(x);

Or just
x^3+2*x ;
In this case variable ‘ans’ is automatically created to which
result is assigned
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Continued …..
•Statement is terminated with ‘;’
•If it is not terminated with ‘;’ , result will be displayed on
screen.
•Statements can be placed on same line if they are terminated
with ‘;’
•Single statement can be continued to next line with three or
more periods e.g. y=x*x+ …..
2*x+3;

•MATLAB is case sensitive.
•who or whos will list variables in current workspace.
•inmem lists compiled m files in current memory.
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Continued…..
•VARIABLE OR FUNCTION CAN BE CLEARED FROM
WORKSPACE
clear variablename
clear functionname
•clear WILL CLEAR ALL NON PERMANENT VARIABLES.
•ON LOGOUT ALL VARIABLES ARE LOST
•‘save’ WILL SAVE ALL VARIABLES IN FILE matlab.mat
•‘load’ WILL RESTORE WORKSPACE TO ITS FORMAL STATE.
•‘save’ and ‘load’ TAKE VARIABLE NAME AND FILENAME AS
OPTIONAL ARGUMENTS.
•edit fun opens the file fun.m in a text editor.

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CONTROL STRUCTURES
IN MATLAB

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RELATIONAL OPERATORS
< LESS THAN
> GREATER THAN
<= LESS THAN OR EQUAL
>= GREATER THAN OR EQUAL
== EQUAL
~= NOT EQUAL
NOTE: = IS USED IN ASSIGNMENT AND = = IS USED IN A
RELATION

LOGICAL OPERATORS
& AND
| OR
~ NOT
RELATIONS MAY BE CONNECTED BY LOGICAL OPERATORS

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OUTPUT OF RELATIONS OPRATION

WHEN APPLIED TO SCALAR, RELATION IS ZERO OR ONE
DEPENDING ON WHETHER THE RELATION IS TRUE OR FALSE
a=3; b=2;
c= ( a>b) ; It means c=1
c=(a<b); It means c=0
a= = b answer is 0
a~=b answer is 1

AND WHEN APPLIED TO MATRICES OF SAME SIZE, RELATION
IS MATRIX OF 0’s and 1’s GIVING VALUE OF RELATION
BETWEEN CORROSPONDING ENTERIES.
d=[1 2]; e=[1 1];
f= (d= =e); It means f=[1 0];

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Control statement

 If ,if else
 For loop
 While loop
 Switch case
 Brake ,continue etc.

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IF

price=4500;
if price >5000,
disp('PRICE IS MORE THAN 5000');
end

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IF ELSE

price=4500;
if price >5000,
else
disp(‘PRICE IS NOT MORE THAN 5000’);
end

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IF ELSEIF
price=4500;
if price >5000,

elseif (1000<=price)&(price <=5000),
disp('PRICE IS BETWEEN 1000 AND 5000');
else
disp('PRICE IS LESS THAN 1000');
end

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WHILE LOOP
var=20;
while var>0,
disp(var);
var=var-1;
end
disp('variable is zero now');
disp(var);

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FOR LOOP

for i=1:10,
disp(i);
end
for i=1:2:11,
disp(i)
end

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Nested For Loop
n=3;
for i=1:n,
for j=1:n,
a(i,j)=5;
end
end
disp(a);

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SWITCH CASE
var1=10;
var2=5;
switch operation
case 'add'
output=var1+var2;
disp(output);
case {'multiply','product'}
output=var1*var2;
disp(output);

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CONTINUED ……….
case {'subtract','sub'}
output=var1-var2;
disp(output);
case 'divide'
output=var1/var2;
disp(output);
otherwise
disp('What else you want?');
end
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CONTINUED…….
case {'subtract','sub'}
output=var1-var2;
disp(output);
case 'divide'
output=var1/var2;
disp(output);
otherwise
disp('What else you want?');
end
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BREAK STATEMENT
var=20;
while var>0,
disp(var);
if var==10
break;
end
var=var-1;
end
str=sprintf('Now variable is %d',var);
disp(str);

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FUNCTION IN MATLAB

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SCALAR FUNCTIONS
•Operate essentially on scalars.
•Operate element-wise when applied to a matrix.
sin asin exp
abs cos acos
log10 log (natural log) sqrt
floor tan atan
rem (remainder) sign
round
A=sin(1)
A=
0.8415
A=sin([1 1.2 1.3 1.4])
A=
0.8415 0.9320 0.9636 0.9854
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VECTOR FUNCTIONS
•OPERATE ESSENTIALY ON VECTOR (ROW OR COLUMN)
•WHEN APPLIED TO MxN MATRIX, OPERATE COLUMN BY
COLUMN TO PRODUCE ROW VECTOR CONTAINING RESULT
OF APPLICATION TO EACH COLUMN.
max sum median
any min prod
mean all sort
std
max([1 2 3])
ans =
3
max([1 2 3
589
7 6 2])
ans =
39 8 9
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MATRIX FUNCTIONS

eig eigenvalues and eigenvectors
chol cholesky factorization
svd singular value decomposition
inv inverse
lu LU factorization
qr QR factorization
rref reduced row echelon form
expm matrix exponential

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STRING FUNCTIONS
strcmp(str1,str2)
strncmp(str1,str2,n)
strcat(str1,str2)
str2num(str)
str2double(str)
num2str(num)
CAT(DIM,A,B) concatenates the arrays A and B along the dimension
DIM.
CAT(2,A,B) is the same as [A,B].
CAT(1,A,B) is the same as [A;B].

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WRITING FUNCTION

function [sum,diff]= addsub(a,b)
%This function returns two outputs, sum
%and difference
sum=a+b;
diff=a-b;
return;

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FUNCTION CONTINUED
function result=perform(operation ,var1,var2)
switch operation
case 'multiply'
result=var1*var2;
case 'add'
result=var1+var2;
case 'subtract'
result=var1-var2;
case 'divide'
result=var1/var2;
otherwise
disp('Only multilply, add,subtract and divide operations are
allowed');
result='error';
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INPUT
name=input('Please enter your name : ','s');
fprintf('nHello %s !n',name);
account=input(' Please enter your account number : ');
if (25 <account)&(account<50)
disp('Welcome');

else
disp('You are not a valid user');
end
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FORMATED OUTPUT
name=‘svits';
age=06;
salary=1800000;
fprintf('n Institute Name : %st Age : %d ….
t Salary : Rs %0.2f',name,age,salary);
fprintf('n I am writing 123456 in exponential ….
form : %e',12356);
a=[1.2 1.3 1.4 1.5 1.6];
fprintf('n %f ',a);
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Thank you

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Basics of programming in matlab

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