Introduction_to_Matlabbanmar k ibrahim a

Introduction to Matlab
Anmar K . Ibrahim
an76mar16@yahoo.com

Introduction to Matlab Sumitha Balasuriya 2
Matlab
• Stands for MATrix LABoratory
• Interpreted language
• Scientific programming environment
• Very good tool for the manipulation of matrices
• Great visualisation capabilities
• Loads of built-in functions
• Easy to learn and simple to use

Matlab Desktop
Command
Window
Workspace /
Current Directory
Command
History
Explore the Matlab Desktop

Variables
• Don’t have to declare type
• Don’t even have to initialise
• Just assign in command window
>>
>> a=12; % variable a is assigned 12
Matlab
prompt
assign
operator
suppress
command
output
comment
operator
Try the same line without the
semicolon and comments

Variables (continued …)
• View variable contents by simply typing the
variable name at the command prompt
>> a
a =
12
>>
>> a*2
a =
24
>>

Workspace
• The workspace is Matlab’s memory
• Can manipulate variables stored in the workspace
>> b=10;
>> c=a+b
c =
22
>>

Workspace (continued …)
• Display contents of workspace
>> whos
Name Size Bytes Class
a 1x1 8 double array
b 1x1 8 double array
c 1x1 8 double array
Grand total is 3 elements using 24 bytes
>>
• Delete variable(s) from workspace
>> clear a b; % delete a and b from workspace
>> whos
>> clear all; % delete all variables from workspace
>> whos

Matlab help commands
• help
>> help whos % displays documentation for the function whos
>> lookfor convert % displays functions with convert in the first help line
• Start Matlab help documentation
>> helpdesk

Matrices
• Don’t need to initialise type, or dimensions
>>A = [3 2 1; 5 1 0; 2 1 7]
A =
3 2 1
5 1 0
2 1 7
>>
square brackets to define matrices
semicolon for next row in matrix

Manipulating Matrices
• Access elements of a matrix
>>A(1,2)
ans=
2
• Remember Matrix(row,column)
• Naming convention Matrix variables start
with a capital letter while vectors or scalar
variables start with a simple letter
A =
3 2 1
5 1 0
2 1 7
indices of matrix element(s)

The : operator
• VERY important operator in Matlab
• Means ‘to’
>> 1:10
ans =
1 2 3 4 5 6 7 8 9 10
>> 1:2:10
ans =
1 3 5 7 9
Try the following
>> x=0:pi/12:2*pi;
>> y=sin(x)

The : operator and matrices
>>A(3,2:3)
ans =
1 7
>>A(:,2)
ans =
2
1
1
A =
3 2 1
5 1 0
2 1 7
What’ll happen if you type A(:,:) ?

Manipulating Matrices
>> A ' % transpose
>> B*A % matrix multiplication
>> B.*A% element by element multiplication
>> B/A % matrix division
>> B./A % element by element division
>> [B A] % Join matrices (horizontally)
>> [B; A] % Join matrices (vertically)
A =
3 2 1
5 1 0
2 1 7
B =
1 3 1
4 9 5
2 7 2
Create matrices A and B and try out the the matrix operators in this slide
Enter matrix B
into the Matlab
workspace

Scripts
• Matlab editor
• Use scripts to execute a series of Matlab
commands
Matlab
Desktop
Press to create
new m-file in the
matlab editor

Scripts(continued)
• Scripts will manipulate and
store variables and matrices
in the Matlab Workspace
(memory).
• They can be called from the
Matlab command line by
typing the (case sensitive!)
filename of the script file.
>> myscript
• Scripts can be opened in the
editor by the following
>> open myscript
Highlight a few lines of your
script by left- clicking and
dragging the mouse over the
lines. Right-click the
highlighted lines and select
Evaluate Selection.
Will be slightly
different in Linux

Functions
• Programming in Matlab.
• Users can write functions which can be called from the command line.
• Functions can accept input variable(s)/matrice(s) and will output
variable(s)/matrice(s).
• Functions will not manipulate variable(s)/matrice(s) in the Matlab
Workspace.
• In Matlab functions closely resemble scripts and can be written in the
Matlab editor. Matlab functions have the function keyword.
• Remember that the filename of a function will be its calling function name.
• Don’t overload any built-in functions by using the same filename for your
functions or scripts!
• Functions can be opened for editing using the open command. Many built-
in Matlab functions can also be viewed using this command.

>> I=iterate(5)
I =
1 4 9 16 25
Functions (continued)
output
input
function name
for statement block
function keyword
help lines for function
Access the comments of
your Matlab functions
>> help iterate Make sure you save changes to the
m-file before you call the function!

>> [i j]=sort2(2,4)
i =
4
j =
2
>>
Functions (continued)
Functions can have many
outputs contained in a matrix
Remember to use the
Matlab help command for
syntax
>> help if
if statement
block

More flow control
Method is linear
>>
i =
4
i =
16
i =
256
While statement block Switch statement block
Without ; to
print output

Debugging
• Set breakpoints to stop the execution of code
>> [i j]=sort2(2,4)
K>>
K>> whos
Name Size Bytes Class
a 1x1 8 double array
b 1x1 8 double array
Grand total is 2 elements using 16 bytes
K>> a
a =
2
K>> return
i =
4
j =
2
Click mouse on the left
of the line of code to
create a breakpoint
local function
workspace
exit debug
mode
Debug menus

Visualisation - plotting data
>> figure % create new figure
>> t=0:pi/12:8*pi;
>> y=cos(t);
>> plot(t,y,‘b.-')
Investigate the function
>> y=A*cos(w*t+phi);
for different values of phi (eg: 0, pi/4, pi/3,
pi/2), w (eg: 1, 2, 3, 4) and A (eg: 1, 0.5, 2). Use
the hold on Matlab command to display your
plots in the same figure. Remember to type
hold off to go back to normal plotting mode.
Try using different plot styles (help plot)
A = amplitude
phi = phase
w = angular frequency = 2*pi*frequency
Plot style

Image Processing using Matlab
Next week …

Useful operators and built-in functions
< ¦ save !
> rand load guide
~= zeros … get
== min ' ' set
>= max { }
<= repmat try
& axis catch
Remember to use the Matlab help command if you get stuck
string
cell
error handling
Operating
system
command
Graphical
user interface
Continue in next line

Tutorial 1
• Login to your workstation, start Matlab and create a working directory
1) Login to Linux using your username/password
2) Open a terminal session by right clicking the mouse on the screen and selecting New Terminal
3) Type the following in the terminal session (do not type the prompt sign > )
> matlab
> mkdir work
4) Type the following in Matlab (do not type the prompt sign >> )
>> cd work
• Explore Matlab! Use the help matlab command to understand the built-in Matlab functions
• Type the code in this handout in Matlab and investigate the results.
• Write a Matlab function fibonacci.m to generate the Fibonacci series. This is generated by starting with zero and one and adding the last two numbers of the
sequence to generate the next number in the series. Fibonacci series:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, ...
• Create an graph of the Fibonacci series using the built-in plot Matlab function. Your graph should resemble figure 1 which contains a plot of the first 20
numbers in the sequence.
• Plot the Fibonacci series in polar coordinates using the built-in Matlab polar function. Eccentricity (rho) should be the Fibonacci number and angle (theta)
should vary with the Fibonacci number’s order in the sequence. Your plot should resemble figure 2 which is a polar plot of the first 10 numbers of the series.
• Exit Matlab by typing quit and logout of Linux.
>> quit
Figure 1
Figure 2

Introduction_to_Matlabbanmar k ibrahim a

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