ELG 3125 - Lab 1 Introduction to MATLAB

ELG 3125 Signal and System Analysis P. 1

ELG 3125 - Lab 1

Introduction to MATLAB

TA: Chao Wang([email protected])

2008 Fall


Do You Speak MATLAB?MATLAB - The Language of Technical Computing


What’s MATLAB ?MATLAB is a program for doing numerical computation. It was originally designed for solving linear algebra type problems using matrices. It’s name is derived from MATrix LABoratory.MATLAB has since been expanded and now has built-in functions for solving problems requiring data analysis, signal processing, optimization, and several other types of scientific computations. It also contains functions for 2-D and 3-D graphics and animation. (Toolboxes)


Starting MATLAB

When starting up the MATLAB program, MATLAB loads and checks that a license is available and throws up a splash screen.


Starting MATLABNext MATLAB’s desktop appears.

•Command Window

•Current Directory

•Workspace Browser

•Command History

•Launch Pad


MATLAB DesktopCommand Window

• The MATLAB environment is command oriented somewhat like UNIX or DOS. A prompt appears on the screen and a MATLAB statement can be entered.

• Use the Command window to enter variables and run functions and M-files.

• When the <ENTER> key is pressed, the statement is executed, and another prompt appears.


MATLAB DesktopCommand Window (cont.)

• If a statement is terminated with a semicolon ( ; ), no results will be displayed. Otherwise results will appear before the next prompt.

• Right is an example from a MATLAB screen.


MATLAB DesktopCommand History

• Statements you enter in the Command window are logged in the Command Histroy.

• Simply double-click the command.


MATLAB DesktopWorkspace Browser

• Consists of the set of all current variables built up during a MATLAB session and stored in memory.

• Add variables to the workspace by using functions, running M-files and loading saved workspaces.


MATLAB DesktopWorkspace Browser (cont.)

• Commands for workspace variables:

who, whos – current variables in workspace

save – save workspace variables to *.mat file

load – load variables from .mat file

clear, clear all – clear workspace variables


MATLAB DesktopCurrent Directory

• File and folder information in the current directory


MATLAB DesktopLaunch Pad

• access tools, demos and documentation


MATLAB Variables

Variable names

• Variable names ARE case sensitive

• Variable names can contain up to 63 characters (as of MATLAB 6.5 and newer)

• Variable names MUST start with a letter followed by letters, digits, and underscores.

(for example: x, y, my_var, Y_2, time_2_frequency)


MATLAB Variables

MATLAB special variables

• ans Default variable name for results• pi Value of π• eps Smallest incremental number• inf Infinity• NaN Not a number e.g. 0/0• i and j i = j = square root of -1• realmin The smallest usable positive real number• realmax The largest usable positive real number


MATLAB Symbols

Some MATLAB symbols

>> prompt. . . continue statement on next line, separate statements and data% start comment which ends at end of line; (1) suppress output

(2) used as a row separator in a matrix: specify range


MATLAB MatricesMATLAB treats all variables as matrices. For our purposes a matrix can be thought of as an array, in fact, that is how it is stored.

Vectors are special forms of matrices and contain only one row OR one column.

Scalars are matrices with only one row AND one column


MATLAB MatricesA matrix with only one row AND one column is a scalar. A scalar can be created in MATLAB as follows:


MATLAB MatricesA matrix with only one row is called a row vector. A row vector can be created in MATLAB as follows (note the commas):


MATLAB MatricesA matrix with only one column is called a column vector. A column vector can be created in MATLAB as follows (note the semicolons):


MATLAB MatricesA matrix can be created in MATLAB as 2-D form (note the commas AND semicolons):


MATLAB MatricesMatrix Operations

• transpose: • subscription:


MATLAB MatricesMatrix Operations (cont.)

• whole row: • whole column:


MATLAB MatricesExtracting a Sub-Matrix

• A portion of a matrix can be extracted and stored in a smaller matrix by specifying the names of both matrices and the rows and columns to extract. The syntax is:

sub_matrix = matrix ( r1 : r2 , c1 : c2 ) ;

where r1 and r2 specify the beginning and ending rows and c1and c2 specify the beginning and ending columns to be extracted to make the new matrix.


MATLAB MatricesExtracting a Sub-Matrix (cont.)


MATLAB MatricesGenerating Matrix from built-in Functions

zeros(M,N)

MxN matrix of zeros

ones(M,N)MxN matrix of ones

rand(M,N)MxN matrix of uniformly distributed random numbers on (0,1)


MATLAB OperatorsArithmetic Operators

+ unary addition- unary subtraction* multiplication/ right division\ left division (56/8=8\56)^ power‘ complex conjugate

transpose

.* element-by-element mult.

./ element-by-element div

.^ element-by-element power

.’ transpose


MATLAB OperatorsRelational and Logical Operators

& AND| OR~ NOT

== equal~= not equal< less than<= less than or equal> greater than>= greater than or equal


MATLAB Flow ControlMATLAB has six basic flow control constructs:

- if-elseif-else statements- switch-case statements- for loops- while loops- break statements: Terminate execution of WHILE

or FOR loop.- continue statements: Pass control to the next

iteration of FOR or WHILE loop.


MATLAB M-Files

Sequences of MATLAB commands can be written to files with the extension “*.m”, called M-files.Entering the name of the file (without the extension) causes automatic execution of all the statements in the file.


MATLAB M-FilesThere are two kinds of M-files

- Scripts, which do not accept input arguments or return output arguments. They operate on data in the workspace. (Simplest form of M-files)

- Functions, which can accept input arguments and return output arguments. Internal variables are local to the function.


MATLAB M-FilesAn example of Script M-files

- Creat a file by the name “myscript.m”

- Contents of “myscript.m”:x=45*pi/180; %convert degrees to radiansa=sin(x); %compute sine 45 degreesb=cos(x); %compute cosine 45 degreesdisp('sin(45*pi/180)='); %print header disp(a); %print result

- Run “myscript.m”:


MATLAB M-FilesAn example of Function M-files

- Create a file by the name “cosgen.m”

- FUNCTION Add new function

- Contents of “cosgen.m”:

function [ y ] = cosgen ( x,a,f,p )% COSGEN genreation of a cosine wave% y = cosgen (s, a, f, p)% y - cosine of x;% a - amplitude;% f - frequency;% p - phase

y=a*cos(2*pi*f*(x+p/(2*pi*f)));

y – output argument

x,a,f,p – input arguments


MATLAB M-FilesAn example of Function M-files (cont.)

- run the “cosgen.m”


MATLAB M-FilesAn example of Function M-files (cont.)

- Hint: All the comments at the beginning of a Function M-file will be displayed as help content.


MATLAB M-FilesEditing M-files through Editor Window

- Use the Editor/Debugger to create and debug M-files, which are programs you write to run MATLAB functions.

- The Editor/Debugger provides a GUI for basic text editing, as well as for M-file debugging.

Create a new M-file: File -> New -> M-file

Open an M-file: File -> Open


MATLAB Built-in FunctionsMATLAB also has many built-in functions

- >> abs(x) Absolute value

- >> exp(x) Exponential value

- >> fix(x) Round towards zero

- >> sqrt(x) Square root

- >> log10(x), log(x) Common (base 10) logarithm, Natural logarithm

- >> round(x), ceil(x) Round towards nearest integer, Round towards plus infinity

- >> sin(x), cos(x) Sine, Cosine

- >> size(x), length(x) Size of array, Length of vector

- >>max(x), min(x) Largest, Smallest component


MATLAB Graphics

MATLAB supports a number of plot types with the ability to create customized graphs.The simplest x-y type plot can be created by “plot(x,y)”To find out about the syntax for any of the plot commands, you can type “help <commandname>”inside of MATLABThe figure plotted will be shown in the Figure Window.


MATLAB GraphicsGraph 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>> axis control axis scaling and appearance


MATLAB GraphicsSome simple examples

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

0 1 2 3 4 5 6 7-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

x = 0:2πS

ine

of x

Plot of the Sine Function


MATLAB GraphicsSome simple examples (cont.)

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

0 1 2 3 4 5 6 7-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1



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)

0 2 4 6 8-1

-0.5

0

0.5

1

0 2 4 6 8-1

-0.5

0

0.5

1



k=0:20;y=binopdf(k,20,0.5);stem(k,y)

binopdf(): Binomial probability density function

0 2 4 6 8 10 12 14 16 18 200

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18


Where to get help?

In Matlab’s prompt type:

• >>help Display help text in Command Window.

• >>lookfor Search all M-files for keyword.

• >>helpwin Online help displayed in the Help window.

• >>helpdesk Comprehensive hypertext documentation.

• >>demos Examples and demonstrations.

• >>doc Display HTML documentation in the Help browser.


Where to get help?

On the web:


End of Lab 1. Thank you.

Any Questions?

Documents

ELG 3125 - Lab 1 Introduction to MATLAB