Matlab Seminar

8/6/2019 Matlab Seminar

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A Seminar On

MATLABThe Language of Technical

Computing

By

Pratik Kamat

[email protected]



WHAT IS MATLAB ?

´ MAT-rix LAB-oratory

´ Developed by The Mathworks, Inc (http://www.mathworks.com))

´ Interactive, integrated, environment

« for numerical computations

« for symbolic computations

« for scientific visualizations

´ It is a high-level programming language



CHARACTERISTICS OF MATLAB

´ Programming language based (principally) on matrices

« Automatic memory management, i.e., you don't have to declarearrays in advance

« Intuitive, easy to use

« Shorter program development time than traditional programming languages such as Fortran and C

« Can be converted into C code via MATLAB compiler for better efficiency

« Slow - an interpreted language ,i.e. .not pre-compiled. Avoid for loops; instead use vector form whenever possible

´ Many application-specific toolboxes available



STARTING MATLAB

Start menu Matlab MATLAB

>> date



GETTING HELP

>> help date

>> helpwin date

helpwin gives you the same information as help, but in a different window.



GETTING HELP (CONTD.)

>> doc date

>> lookfor date % search for keywords that best describe the function

>> Ctrl+C % stop Matlab from running

>> clc % clear screen



SPECIAL CHARACTERS

´ >> % default command prompt

´ % % comment - MATLAB simply ignores anything to the right of this

sign (till the end of the line).

>> % my comment

´ ; % semicolon at the end of the line will prevent MATLAB from

echoing the information you type on the screen.

>> a=20

>> B=20;



CREATING VARIABLES

´ Matlab as a calculator:

´ >>2+5

´ >>7*10+8

´ >>5^2

´

µans¶ - "answer", used in MATLAB as the default variable.



DEFINING YOUR OWN VARIABLES

� When Matlab comes across a new variable name - it automatically creates

it.

� Begins with a LETTER, e.g., A2z.

� Can be a mix of letters, digits, and underscores (e.g., vector_A, but not

vector-A)� Not longer than 31 characters.

� No spaces

� Different mixes of capital and small letters = different variables.

For example: "A_VaRIAbLe", "a_variable", "A_VARIABLE", and

"A_variablE

� >> String=µthis is a string¶



TAKING USER DEFINED INPUTS

� Matlab uses the function µinput¶ to accept user-defined inputs

� E.g. y=input(µEnter any Value¶);

Now, if a user has to enter a Vector,then he enters[ 1 2 4 5]

For a matrix, the syntax is as follows

[1 2 3 4 5 ; 9 8 7 6 5]



PRACTICE PROBLEM

Write a Program to accept the length of side of a square and

display its area.

Write a Program to accept three numbers from the user and todisplay their average.



SOLUTION

x=input(¶Enter the first number·);

y=input(¶Enter the second number·);

z=input(¶Enter the third number·);

Average=(x+y+z)/3;

side=input(¶Enter the length of the side·);

Area=side*side;



LISTING & CLEARING VARIABLES

>> whos

>> clear, clear all %clear variables from memory

>> clc %clears the screen

>> a=10

>> b = 20

>> the_average = (a + b ) / 2



CREATING VECTORS

R ow separator:

space/coma (,)

Creating sequences:

� From : jump: till

� linespec(X1, X2, N)

generates N points between

X1 and X2.

Coulmn separator:Semicolon (;)

Indexing Begins at 1



CREATING MATRICES

� Matrices must be rectangular.

� Creating random matrices:

2-by-4 random matrix

(2 rows and 4 columns).



CREATING MATRICES (CONT.D)

� You can combine existing vectors as matrix elements:

� You can combine existing matrices as matrix elements:



INDEXING INTO A MATRIX

>> B=A(3,1);

>> A(:,end)=[1;7;3;8;4];

� The row number is first, followed by the column number.



PRACTICE PROBLEM

Write a Program to accept three numbers from the user and to

display their average.



SOLUTION

x i t(¶ t r t rs·);

v r g (x(1) x(2) x( ))/l gt (x)



LI LGEBRA ERATI



MATRIX MULTIPLICATION

´ Inner dimensions must be equal

´ Dimension of resulting matrix = outermost

dimensions of multiplied matrices

´

Resulting elements = dot product of the rows of the st matrix with the columns of the nd matrix



VECTOR MULTIPLICATION

Type the following:

>>a=[2 3]

>>b=[3 2]

>>a*b

>>a.*b

>>a.*b¶

>>a*b¶



PRACTICE PROBLEM

Write a Program to display the squares of all numbers from 1 - 20



SOLUTION

X=1:1:10;

sq=X.*X



STRING ARRAYS

´ Created using single quote delimiter (')

� Indexing is the same as for numeric arrays



STRING ARRAY CONCATENATION



WORKING WITH STRING ARRAYS



EXAMPLE: SOLVING EQUATIONS

´ Solve this set of simultaneous equations:

Ax=B, x=?



EXAMPLE: SOLVING EQUATIONS

´ Solve this set of simultaneous equations:

Ax=B, x=?



MATLAB DEBUGGER

´ Automatically saves files as ASCII text files for you.

´ Scripts in MATLAB has the ".m" suffix.

´ They are also called "M-files".

Open Matlab Editor:

´ File New M-file OR :

´ >> edit

Run



FLOW CONTROL CONSTRUCTS

´Logic Control:

«IF / ELSEIF / ELSE

«SWITCH / CASE / OTHERWISE

Íterative Loops:

«FOR

«WHILE



THE IF,THE IF, ELSEIF ELSEIF AND ELSE AND ELSE STATEMENTS STATEMENTS

if I == J

A(I,J) = 2;

elseif abs(I-J) == 1

A(I,J) = -1;

else

A(I,J) = 0;

end

� Works on Conditional statements

� Logic condition is µtrue¶ if its different then 0.

� ELSEIF does not need a matching E ND, while ELSE IF does.

if I == J

A(I,J) = 2;

else if abs(I-J) == 1

A(I,J) = -1;

else

A(I,J) = 0;

end %else if

end %if



BOOLEAN OPERATORS & INDEXING



SWITCH, CASE, AND OTHERWISE SWITCH, CASE, AND OTHERWISE

switch input_num

case -1input_str = 'minus one';

case 0input_str = 'zero';

case 1input_str = 'plus one';

case {-10,10}input_str = '+/- ten';

otherwiseinput_str = 'other value';

end

´More efficient than elseif statements

Ónly the first matching case is executed



P ROBLEM P ROBLEM

´ Build a program which receives a variable x and its units (mm, cm, inch, meter)

and calculates Y- it¶s value in centimeters units.

´ Use switch case.

´ 1 Inch = 2.54 cm

´ Save the file under units.m



SOLUTION SOLUTION

x = 3.0;

units = 'mm';

switch units

case {'in','inch'}

y = 2.54*x % converts to centimeters

case {'m','meter'}y = x*100 % converts to centimeters

case { 'millimeter','mm'}y = x/10;

case {'cm','centimeter'}y = x ;

otherwise

disp (['unknown units:' units])

End

y



� Similar to other programming languages

� Repeats loop a set number of times (based on index)

� Can be nested

� Each loop is closed with end.

THE FOR LOOP THE FOR LOOP

N=10;

for I = 1:2:N

for J = 1:N A(I,J) = 1/(I+J-1);

end

end



P ROBLEM P ROBLEM

´ Build a program to generate the factorial of a number.

´ Use for loop



SOLUTION SOLUTION

n=5;

facto=1;

for i=1:n

facto=facto*n;

end

facto



THE WHILE LOOP THE WHILE LOOP

I=1; N=10;

while I<=N

J =1;

while J<=N

A(I,J)=1/(I+J-1);J =J+1;

end

I=I+1;

end

� Similar to other programming languages

� Repeats loop until logical condition returns FALSE.

� Can be nested.

� Stopping infinity loop:

Ctrl+C

Ctrl+break



ARRAY OPERATIONS



LINE PLOTS IN TWO

DIMENSIONS´ Plot (x,y)

´ makes a two-dimensional line plot for each point in X and its

corresponding point in Y: (X( ),Y( )), (X( ),Y( )), (X(3),Y(3)), etc., and

then connect all these points together with line.

´ Example:

´ >> x= : :5;

´ >>Y=[ 7 0 -8 6];

´ >> plot (x,y);

´ >> xlabel (¶label for x-axis·)

´ >> ylabel (¶label for y-axis·)

´ >> title (¶title·)



MULTIPLE PLOTS´ C

heck the following:´ x_points = [- 0 : .05 : 0];

´ plot(x_points, exp(x_points)); % plot in Blue (default)

´ grid on

´ hold on

´ plot(x_points, exp(.95 .* x_points), 'm');% plot in Magenta

´ plot(x_points, exp(.85 .* x_points), 'g'); % plot in Green

´ plot(x_points, exp(.75 .* x_points), 'p'); % plot a star

´ hold off

´ xlabel('x-axis'); ylabel('y-axis');

´ title('Comparing Exponential Functions');

´ legend (' ', ' ', '3', '4')

- 10 -5 0 5 10 0

0. 5

1

1. 5

2

2. 5 x 10

4

x-axis

y - a x i s

Comparing E xponential Functions

1

2

3

4



SUBPLOTS

´Multiple plots in the same window, each

with their own axes.

´ Subplot (M,N,P)´M ² rows

´ N - columns

´ P ² number of subplotin the figure

Subplot (2,2,1)



MORE ABOUT FIGURES

´ Figure % Open a new figure without closing old

figures

´ Figure (i) % Open the i-th figure

´ Close all % close all open figures

´ axis ([xmin xmax ymin ymax]) % sets scaling for

the x- and y-axes on the current plot.



SPECIAL GRAPH ANNOTATIONS (TEX)



PLOT EDITOR TOOLBAR



EXERCISE

´ x (1, 1. , 1.1, 1.1 « )

´ si (x)

´ Z l g(x)

´ P t y r i t titl

´ Hi t: c c t c f cti ´Li S cµ.

Create the following:

1 1 .

¡ ¡ .

¢ ¢ .

£ £ .

¤ 1

-0 .

0

0 .

1

1 .

¡

M ¥

r ¦

v' §

̈ r

¦

©

h

§ i

(

)

l ̈ (

)



SOLUTION

x= :0.05:5;

y=sin(x);

z=log(x);

hold onplot (x,y,'-.r*')

plot (x,z,'-.go')

hold off

title ( ep's graph');

xlabel ('x')

ylabel ('y')

legend ('sin(x)', 'log(x)');



EXERCISE

Plot the following graph:

y=1 for x>0

=-1 elsewhere



SOLUTION

x=-3:0.0 :3

for i= :length(x)

if x(i) > 0

y(i) = ;else

y(i) = - ;

end

end

plot(x,y)



MORE EXERCISE

´ Make a 3 three-dimensional graph of (x,y,z) ² useMatlab help.

´ Make two separate -D graphs, with separate axis, in the same

window: y vs. x, and z vs. x.

´ Use the same x,y,z as defined in the previous exercise

1

2

3

4

5

-1

-0.5

0

0. 5

10

0. 5

1

1. 5

2

x

3D graph

y

z

1 2 3 4 5 -1

-0.8

-0.6

-0.4

-0.2

0

0. 2

0. 4

0. 6

0. 8

1sin(x)

x

y = s i n ( x )

1 2 3 4 5 0

0. 2

0. 4

0. 6

0. 8

1

1. 2

1. 4

1. 6

1. 8

x

log(x)

z



SOLUTION

´ 3-D graph:

´ >> plot3(x,y,z)

´

>> grid´ >> xlabel ('x')

´ >> ylabel('y')

´ >> zlabel('z')

´ >> title ('3Dgraph')

� Subplots

>> subplot (1,2,1);

>> plot(x,y);

>> title ('sin(x)');>> xlabel('x');

>> ylabel('y=sin(x)');

>> grid;

>> subplot (1,2,2);

>> plot(x,z);>> xlabel('x');

>> title ('log(x)');

>> grid;

>> ylabel ('z');

GRAPHICAL USER INTERFACE



GRAPHICAL USER INTERFACE

DEVELOPMENT ENVIRONMENT (GUIDE)

´ Graphical User Interface Design Environment provides a set of tools for creating graphical user interfaces (GUIs).

´ GUIDE automatically generates an M-file that controls how the GUI

operates.

´ StartingGUIDE:

>> guide Push

buttons

Static

text

Pop-up menu

axes



GUIDE TOOLS ± THE LAYOUT

EDITOR

� In the Quick Start dialog, select the Blank GUI (Default) template

� Display names of components: File preferences Show names in component palette

� Lay out your GUI by dragging components

(panels, push buttons, pop-up menus, or axes)

from the component palette, into the layout area

Drag to

resize

Component

panel

Layout area



USING THE PROPERTY INSPECTOR

� Labeling the Buttons

� Select Property Inspector from the View menu.

� Select button by clicking it.

� Fill the name in the String field.

Activate

GUI

Property

Inspector



PROGRAMMING A GUI

´ Callbacks are functions that execute in response to some action bythe user.

´ A typical action is clicking a push button.

´ You program the GUI by coding one or more callbacks for each of its

components.

´ A GUI's callbacks are found in an M-file that GUIDE generatesautomatically.

´ Callback template for a push button:



HANDLES STRUCTURE

´ Save the objects handles: handles.objectname

´ Save global data ± can be used outside the function.

´ Example: popup menu:

´ Value ± user choice of the popup menu



HANDLES STRUCTURE(CONTD.)

´ Use ´strµ as the string pointer

´ Static Text

« set(handles.text ,·String·,str)

´ Radio Button

« set(handles.radiobutton,·Value·,0)

´ Pop-Up Menu

« get(handles.radiobutton,·Value·)



SCRIPT M-FILES

´Standard ASCII text filesĆontain a series of MATLAB expressions

Á script does not define a new workspace

% Comments start with "%" character

pause % Suspend execution - hit any key to continue.

keyboard % Pause & return control to command line.

% Type "return" to continue.

break % Terminate execution of current loop/file.

return%

Ex

it current function% Return to invoking function/command line.

Continue % go to next iteration

Input % Prompt for user input



A SIMPLE SCRIPTS

% a simple MATLAB m-file to calculate the

% square root of an input numbers.

my_num=input('insert a number');% now calculate the square root of the number and print

it out:

square_root = sqrt(my_num)

Write a program which receives a number from the user,calculates it¶s square root (use µsqrt¶ command) and displays

the result.

save the script as "square_root_script.m" in your own folder



RUNNING SCRIPTS

´ >> square_root_script

´ The header - comments you place at the beginning of your scripts will bereturned to users when they get help for your script.

´ >> help square_root_script

´ Note: The variables defined in the script remain in the workspace even

after the script finishes running.´ Creating comments: ctrl+r, or right click on the mouse, or

%{

coment

coment

%}



RUNNING SCRIPTS (CONTD.)

´ Find and Replace ± ctrl+F

´ Key words

´ Wrong use of key words

´ Indenting: Ctrl+I



FUNCTIONS

´ Functions describe subprograms

«Take inputs, generate outputs

«Have local variables (invisible in global workspace)

Ćore MATLAB (Built-in) Functions«sin, abs, exp, ...

Can¶t be displayed on screen

´MATLAB-supplied M-file Functions

«mean, linspace, «

Ca be displayed on screen

´ User-created M-file Functions



STRUCTURE OF A FUNCTION FILE

function y = mean(x)

% ME AN Average or mean value.

% For vectors, ME AN(x) returns the mean value.

% For matrices, ME AN(x) is a ro w vector

% containing the mean value of each column.

[m,n] = size(x);

if m == 1

m = n;

end

y = sum (x)/ m ;

Keyword: function Function Name (same as file name .m)

Output Argument(s) Input Argument(s)

Online Help

MATLABCode

»

output_ value

=mean

(input_

value)

Command Line Syntax



MULTIPLE INPUT AND OUTPUT

ARGUMENTS

function r = ourrank(X,tol)% OURRANK Rank of a matrix

s = svd (X);if (nargin == 1)

tol =

max(size

(X))*s

(1)*eps

;

end

r = sum (s > tol); function [mean,stdev] = ourstat(x)

% OURSTAT Mean & std. deviation

[m,n] = size(x);

if m == 1

m = n;end

mean = sum (x)/ m ;

stdev = sqrt(sum (x.^2)/ m ± mean.^2);

Multiple Input

Arguments ( , )

Multiple Output

Arguments [ , ]

» R ANK = ourrank(rand (5),0.1);

» [ME AN,STDEV] = ourstat(1:99);



MATLAB CALLING PROPERTY

High

variable

built-in function

subfunctionprivate function

MEX-file

P-file

M-file

Low

» cos='This string.';

» cos(8)

ans=

r

» clear cos

» cos(8)

ans =

-0.1455



MATLAB IN P UT MATLAB IN P UT

To read files in

´ if the file is an ascii table, use ́ loadµ

´ if the file is ascii but not a table, file I /O needs

´fopenµ and ´fcloseµ

´ Reading in data from file using fopen dependson type of data (binary or text)

´ Default data type is ´binaryµ

´ Images can be opened using ímshowµ and canbe read using ímreadµ

ADD PATH TO RECOGNISE



ADD PATH TO RECOGNISE

WORKSPACE

´ >> addpath C:\Docu .\ Somedirectory

´ Set path



THANK YOU

Documents

Matlab Seminar