Matlab Tutorial.ppt

Introduction to Matlab by Mr. M. Ravi, Asst. Professor, Dept, of E.C.E.

What is Matlab? • Matlab is basically a high level language which has many specialized toolboxes for making things easier for us Assembly High Level Languages such as C, Pascal etc. Matlab

What are we interested in? • Matlab is too broad for our purposes in this course. • The features we are going to require is Matlab Command Line m-files functions mat-files Command execution like DOS command window Series of Matlab commands Input Output capability Data storage/ loading

Physical Problem Mathematical Models Solving Mathematical Equations

Introduction • MATLAB (short for MATrix LABoratory) is a powerful computing environment that handles anything from simple arithmetic to advanced data analysis. • At its core is the matrix as its basic data type. • Combined with extensive maths and graphics functions, complicated calculations can be carried out by specifying only a few simple instructions. • MATLAB can be used to do anything your scientific calculator can do, and more. • The installations in the computer labs include tool boxes that include functions for electrical engineering related tasks, such as signal processing and system analysis.

Introduction. . . . • You can plot your data in a multitude of visualizations as well. • Computations can be carried out in one of three ways: 1. Directly from the command line, 2. by writing a script that carries out predefined instructions, or 3. by writing your own functions.

Introduction . . . • Writing your own functions is much like programming in other languages, except that you have the full resources of MATLAB’s functions at your disposal, making for very compact code. The MATLAB-6 and above environment has several windows at your disposal. • Command Window: The main window is the command window, where you will type all your commands, for small programs.

Desktop Tools • Command Window – type commands • Workspace – view program variables – Clear/clear all is used to clear the workspace window – double click on a variable to see it in the Array Editor • Command History – view past commands – save a whole session using diary • Editor Window To write a program • Current Directory Window

Matlab Screen • Command Window – type commands • Current Directory – View folders and m-files • Workspace – View program variables – Double click on a variable to see it in the Array Editor • Command History – view past commands – save a whole session using diary

Command History * A command history, which contains a list of all the commands that you have typed in the command window. * This makes it easy to cut and paste earlier lengthy commands, saving you the effort of typing it over again. * This window can also display the contents of the current directory.

Workspace • The third window displays one of two things: * The launch pad from which you can browse the installed toolboxes and launch various tools as well as view demonstrations, and * The workspace, which lists all the variables that are currently in memory as well as their sizes.

Vectors and Matices and their Manipulation

Definition of Vectors & Matrices • MATLAB is based on matrix and vector algebra; even scalars are treated as 1x1 matrices. Therefore, vector and matrix operations are as simple as common calculator operations. • Vectors can be defined in two ways. * The first method is used for arbitrary elements: v = [1 3 5 7]; creates a 1x4 vector with elements 1, 3, 5 and 7. * Note that commas could have been used in place of spaces to separate the elements. that is v=[1,3,5,7]; • Additional elements can be added to the vector: v(5) = 8; yields the vector v = [1 3 5 7 8].

• Previously defined vectors can be used to define a new vector. For example, with ‘v’ defined above a = [9 10]; b = [v a]; creates the vector b = [1 3 5 7 8 9 10].

Second Method • The second method is used for creating vectors with equally spaced elements: t = 0: 0.1:10; creates a 1x101 vector with the elements 0, .1, .2, .3,...,10. Note that the middle number defines the increment. • If only two numbers are given, then the increment is set to a default of 1: For ex. k = 0:10; creates a 1x11 vector with the elements 0, 1, 2, ..., 10.

* Matrices are defined by entering the elements row by row: M = [1 2 4; 3 6 8; 2 6 5]; creates the matrix * Transpose of M is denoted by M’, and displays as *The inverse of M is M-1 denoted in Matlab as M^-1and displays as * M(2,3) displays the element of second row and third column

Arithmetic Operations • When applying addition, subtraction, multiplication and division between a scalar (that is a single number) and a vector we use +, -, *, and / respectively. Let Then a + b gives a - b gives

aXb in Matlab a*b displays In Matlab a.*b gives element wise multiplication a+2 gives

Algebraic manipulations • Scalar Calculations. The common arithmetic operators used in spreadsheets and program-ming languages such as BASIC are used in ‘Matlab'. • In addition a distinction is made between right and left division. The arithmetic operators are

Operators (relational, logical) = = equal ~= not equal < less than <= less than or equal > greater than >= greater than or equal & AND | OR ~ NOT 1  pi 3.14159265… j imaginary unit, i same as j

Special Matrices • null matrix: M = [ ]; • nxm matrix of zeros: M = zeros(n,m); nxm matrix of ones: M = ones(n,m); nxn identity matrix: M = eye(n);

Help, Document and Demos • Matlab provides excellent tutorials that are accessible by typing >>demo • The Basic matrix operations tutorial under the Matrices tutorial, the Image Processing and Signal Processing tutorial under Toolboxes are highly recommended. • To get information on a particular function of Matlab, we type >>help function_name Example: >> help fft >> help mean

Getting Help The Help pull-down menu gives you access to all the help pages included with MATLAB.

• Comments in Matlab must be proceeded by % % This is a comment in Matlab. • To define a function in Matlab, we first create a function with the name of the function. *We then define the function in the file. *For example, the Matlab documentation recommends stat.m written as: function [mean,stdev] = stat(x) % This comment is printed out with help stat n = length(x); % assumes that x is a vector. mean = sum(x) / n; % sum adds up all elements. stdev = sqrt(sum((x - mean).^2)/n);

Viewing Matlab Matrices as one Dimensional Arrays • Convert multi-dimensional to a one-dimensional array by simply using array_name(:) » a(:) ans = 1 4 7 2 5 8 3 6 9 Note that the elements in the one-dimensional array are arranged column by column, not row by row. This is the same convention that is used for two dimensional arrays in Fortran, and this will also be the convention that we will adopt for representing two dimensional arrays in C++.

Displaying and Printing in Matlab • To plot an array or display an image, select the figure using: » figure(1); % select the figure to display. » clf % clear the figure from any % previous commands. • and use plot for displaying a one-dimen-sional array: » plot ([3 4 5 3 2 2]); % plots broken-line graph. • or use imagesc for displaying a two dimensional array (image):

One-dimensional random access iterator (using an index array) [1 5 9 2 6 10 3 7 11 4 8 12] » I=[1 5 8 10]; % indices apply to one-dimensional array a(:) » a(I) ans = 1 6 7 4 – two dimensional iterators » a(1:2,1:3) ans = 1 2 3 5 6 7 .

Working with Memory in Matlab • To keep track of how memory is allocated, we use whos » b=[34 54 56]; » a=[2 3 56]; » whos Name Size Bytes Class a 1x3 24 double array b 1x3 24 double array Grand total is 6 elements using 48 bytes We may then get rid of unwanted variables using clear » clear a; % removes the variable a from the memory. • We can use clear all to remove all variables from memory (and all functions and mex links) and close all to close all the figures and hence save a lot of memory.

• Since Matlab supports dynamic memory allocation, it is possible to make inefficient use of the memory due to memory fragmentation problems. In this case, the pack command can be used to defragment the memory and help reclaim some of the memory. • To use memory efficiently, it is best to avoid changing the number of elements in an array during execution. It is best to • preallocate arrays before using them. To this end we can use zeros and ones: » a=zeros(3,4); % a two-dimensional 3x4 zero matrix. » b=ones(1,5); % an array of 5 elements of value 1.

Evaluating one-dimensional functions in Matlab • To evaluate one-dimensional functions in Matlab we need to specify the points at which we would like our function to be evaluated at. • We can use either the built-in colon notation to specify the points » t=-1:0.5:1 t = -1.0000 -0.5000 0 0.5000 1.0000 or use linspace( ) » t=linspace(-2,4,5) % generates 5 points % between -2 and 4 t = -2.0000 -0.5000 1.0000 2.5000 4.0000 or use logspace( )

Evaluating one-dimensional functions in Matlab (contd) • In general, all numbers in Matlab are double. Complex numbers are represented by multiplying the imaginary part by 1i. For example, 1+3j can be represented by 1+1i*3 or 1+3i. • All the well-known mathematical functions are defined in Matlab, and but they apply to to each element in the vector directly. • For example, cos([2 3 4]) is equivalent to [cos(2) cos(3) cos(4)].

Evaluating two-dimensional functions in Matlab • To evaluate two-dimensional functions in Matlab we use the built-in function meshgrid ( ) with the ranges for x and y; eg: » [x,y]=meshgrid(0.1:0.1:0.3, 0.2:0.1:0.4) yields the matrices x and y given by: x = 0.1 0.2 0.3 0.1 0.2 0.3 0.1 0.2 0.3

y = 0.2 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.4 • We may then apply any binary operation to x and y provided that we preceed each operation with a period. • For example x.*y represents the matrix where each element of x multiplies each element of y. • Similarly, exp(x.^2+y.^2) represents the matrix resulting from applying exp( ) to the sum of the squares of each of the elements of x and y.

Flow Control • if • for • while • break • ….

Control Structures • If Statement Syntax if (Condition_1) Matlab Commands elseif (Condition_2) Matlab Commands elseif (Condition_3) Matlab Commands else Matlab Commands end Some Dummy Examples if ((a>3) & (b==5)) Some Matlab Commands; end if (a<3) Some Matlab Commands; elseif (b~=5) Some Matlab Commands; end if (a<3) Some Matlab Commands; else Some Matlab Commands; end

Control Structures • For loop syntax for i=Index_Array Matlab Commands end Some Dummy Examples for i=1:100 Some Matlab Commands; end for j=1:3:200 Some Matlab Commands; end for m=13:-0.2:-21 Some Matlab Commands; end for k=[0.1 0.3 -13 12 7 -9.3] Some Matlab Commands; end

Control Structures • While Loop Syntax while (condition) Matlab Commands end Dummy Example while ((a>3) & (b==5)) Some Matlab Commands; end

Generation and plotting of basic signals

To make a graph of y = sin(t) on the interval t = 0 to t = 10 we do the following: >> t = 0:0.3:10; >> y = sin(t); >> plot(t,y) ;

Matlab Graphics x = 0:pi/100:2*pi; y = sin(x); plot(x,y) xlabel('x = 0:2pi') ylabel('Sine of x') title('Plot of the Sine Function')

Multiple Graphs t = 0:pi/100:2*pi; y1=sin(t); y2=sin(t+pi/2); plot(t,y1,t,y2) grid on

Multiple Plots t = 0:pi/100:2*pi; y1=sin(t); y2=sin(t+pi/2); subplot(2,2,1) plot(t,y1) subplot(2,2,2) plot(t,y2)

• Second, I can plot several different sets of data together: >> x = 0 : 0.1 : 10; >> y = sin(x); >> z = cos(x); >> plot(x, y, x, z);

• Another useful command is axis, which lets you control the size of the axes. If I've already created the plot with both sine and cosine functions, I can resize it by typing >> axis([-5, 15, -3, 3]); which changes the plotting window so it looks like this:

• f (x)=sin (x)3 +cos(3x) • over one period syms x; ezplot(sin(x)^3+ cos(3*x), [-pi pi], 1); grid on;

Continuous and Discrete time plots k=0:20; y=binopdf(k,20,0.5); plot(k,y) k=0:20; y=binopdf(k,20,0.5); stem(k,y)

Commonly Used Mathematical Functions

Using Matlab Editors • Very small programs can be typed and executed in command window. • Large programs on other hand can be used the Matlab editor. • The complete program can be typed in the Matlab editor and saved as ‘file_name.m’, and can be retrieved when-ever necessary. • You can execute either directly from editor window or type the file name in the command window and press the enter button.

Creating, Saving, and Executing a Script File % CIRCLE - A script file to draw a pretty circle function [x, y] = prettycirclefn(r) % CIRCLE - A script file to draw a pretty circle % Input: r = specified radius % Output: [x, y] = the x and y coordinates angle = linspace(0, 2*pi, 360); x = r * cos(angle); y = r * sin(angle); plot(x,y) axis('equal') ylabel('y') xlabel('x') title(['Radius r =',num2str(r)]) grid on

Graph Functions (summary) • plot linear plot • stem discrete plot • grid add grid lines • xlabel add X-axis label • ylabel add Y-axis label • title add graph title • subplot divide figure window • figure create new figure window • pause wait for user response

• clc: clear command window • clear all: clear all variables in workspace window • close all: closes all previous figure windows

Random Numbers x=rand(100,1); stem(x); hist(x,100)

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