Lab 1 of COMP 319Lab 1 of COMP 319

An Introduction to MATLAB

Lab tutor : Dennis Yang LIU

Email: csygliu@comp.polyu.edu.hk

Lab 1: Sept. 11, 2014

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Outline of Lab 1

• Introduction to the Lab

• Matlab overview

• Basic manipulation in Matlab

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Outline of Lab 1

• Introduction to the Lab

• Matlab overview

• Basic manipulation in Matlab

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Introduction to the Lab

Schedule DateLab 1 Sept 11 (Thur ) and Sept 16 (Tue )Lab 1 Sept. 11 (Thur.) and Sept. 16 (Tue.)Lab 2 Sept. 18 (Thur.) and Sept. 23 (Tue.)Lab 3 Sept. 25 (Thur.) and Sept. 30 (Tue.)Lab 4 Oct. 7 (Tue.) and Oct. 9 (Thur.) Lab 5 Oct. 14 (Tue.) and Oct. 16 (Thur.) Lab 6 Oct. 21 (Tue.) and Oct. 23 (Thur.) ( ) ( )Lab 7 Oct. 28 (Tue.) and Oct. 30 (Thur.) Lab 8 Nov. 4 (Tue.) and Nov. 6 (Thur.) L b 9 N 11 (T ) d N 13 (Th )Lab 9 Nov. 11 (Tue.) and Nov. 13 (Thur.)

Lab 10 Nov. 18 (Tue.) and Nov. 20 (Thur.) Lab 11 Nov. 25 (Tue.) and Nov. 27 (Thur.)

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Lab 12 Dec. 2 (Tue.) and Dec. 4 (Thur.)

Introduction to the Lab

• Time and place of our labs– Thur. 16:30 – 17:20 PQ 604B– Tue. 09:30 – 10:20 PQ 606

Th l b ill i l f M l b• The lab will mainly focus on Matlab– Basic concepts and useful skills of Matlab (6 labs)– Instructions to the lab project (6 labs: instructions and self-studies)p j ( )

• Directory of lab material– http://www4.comp.polyu.edu.hk/~csyliu/course/comp319/main.ht

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Outline of Lab 1

• Introduction to the Lab

• Matlab overview

• Basic manipulation in Matlab

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Matlab Overview

• What is Matlab?

• Strengths of Matlabg

• Weaknesses of Matlab

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What is Matlab?

• Matlab– MATrix LABoratory

• The name is derived from MATrix LABoratory.

• A programming language for doing numerical computation.

• Originally designed for solving linear algebra type problems using matrices (suitable for image and video processing).

– Functionality of Matlab • built-in functions

• for solving problems requiring data analysis signal processing• for solving problems requiring data analysis, signal processing, optimization, and several other types of scientific computations.

• also contains functions for 2-D and 3-D graphics and animation.

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What is Matlab – con’t

C id i M tl b t h• Considering Matlab at home

– Standard edition• Available for roughly 2 thousand dollars• Available for roughly 2 thousand dollars

– Student edition• Available for roughly 1 hundred dollars.• Some limitations, such as the allowable size of a matrix

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Strengths of Matlab

M l b i l i l l• Matlab is relatively easy to learn• Matlab code is optimized to be relatively quick when

performing matrix operationsperforming matrix operations• Matlab may behave like a calculator or as a programming

language• Matlab is interpreted, errors are easier to fix

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Weaknesses of Matlab

M tl b i i t t d l ( ki it f th t• Matlab is an interpreted language (making it for the most part slower than a compiled language such as C)

• Matlab is NOT a general purpose programming languageMatlab is NOT a general purpose programming language

• Matlab is designed for scientific computation and is not suitable for some things (such as parsing text)g ( p g )

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Outline of Lab 1

• Introduction to the Lab

• Matlab overview

• Basic manipulation in Matlab

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Basic manipulation of Matlab

• Opening and closing Matlab

• The Matlab user interface

• M-file building, saving and running

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Opening and closing Matlab

• Opening Matlab (for Windows XP):Single click ‘Start’ then– Single click Start , then

– Single click ‘Run’, then – Input ‘nalwin32’, then – Double click ‘COMP’, then– Double click ‘Network Application Packages’, then– Double click ‘Statistical & Mathematical’, then,– Double click ‘Matlab’– Select one version (e.g., R2012a), double click to open

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Opening and closing Matlab

• Opening Matlab (for Windows 7):Single click ‘Start’ then– Single click Start , then

– Single click ‘Computer’, then – Double click disk ‘Y’, then– Double click ‘Win32’, then– Double click ‘Matlab’– Select one version (e.g., R2012a), then( g , ),– Double click ‘matlab.exe’ to open

• Closing MatlabT ‘ ’ ‘ ’ h M l b– Type ‘exit’ or ‘quit’ at the Matlab prompt; or

– Click the close icon ‘x’ in the top-right corner of the screen

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Matlab user interface

Command

Workspace

Command Window

CommandCommand History

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Matlab user interface – con’t

• Command Window• Command Window– type commands

• Workspace• Workspace– view program variables– ‘clear’ to clear

d bl li k i bl t it i th A Edit– double click on a variable to see it in the Array Editor

• Command Historyi d– view past commands

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Using the Command Window

• Do it yourself

1. To compute the value of 52, type this command:>> 5^2The following output will be displayed:The following output will be displayed:ans =

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2. To find the cosine of pi, type:>> cos(pi)which result in the following output:g pans =

-1

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Note: ‘ans’ is the default variable name given by Matlab.

Using the Command History

• Do it yourself

In the command window, type:

>> clc

This will clear the command window but leave the data in the command history. Try double-click:

cos(pi)

This will result in the following display in the command window:

ans = -1

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Using the Workspace

• Do it yourself

• Enter the following two-dimensional matrix in the command window:

>> c= [1,2,3,4; 10,20,30,40; 5,10,15,20];

• c should now be listed in the workspace window. • Double clik it An array editor will be listed above the• Double clik it. An array editor will be listed above the

command window. • Then you can add or change values in the array editor.

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Some useful notes• The Matlab environment is command oriented somewhat like UNIX.

• A prompt (>>) appears on the screen and a Matlab statement can be• A prompt (>>) appears on the screen and a Matlab statement can be entered.

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

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

» a=5;» b=a/2

b =

2.5000

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Some useful notes – con’t

• In Matlab, the equal sign ( = ) is used to assign values to the variables. It does not mean ‘equal to’.

• In Matlab environment ‘equal to’ is expressed by two consecutive• In Matlab environment, equal to is expressed by two consecutive equal signs ( == ).

>> x = 5 means that assigning the value 5 to the variable x.

>> x == y means that the value of x is equal to the value of y.

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Some useful notes – con’t

M tl b V i bl N

• Variable names are case sensitive

Matlab Variable Names

• 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.

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Some useful notes – con’t

• Matlab has some special (reserved) words that you may• Matlab has some special (reserved) words that you may not use…

for switchendifwhile

continueelsetrywhile

functionreturn

trycatchglobal

elseifcaseotherwise

persistentbreak

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Matlab Help

• Different ways to find information

– help

– help general, help mean, sqrt...

– click ‘help’ iconp

– Search information from the internet via google

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Matlab Help

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Some other useful Matlab commands

• who List known variables• whos List known variables plus their sizep• clear x y Clear variables x and y from workspace• clear Clear all variables from workspace• clc Clear the command indo• clc Clear the command window

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M-file building and saving

• The command window offers an environment similar to a scratch pad.

• Using the command window allows you to save theUsing the command window allows you to save the values you calculate, but not the commands used to generate those values.

• If you want to save the command sequence you will• If you want to save the command sequence, you will need to use the edit window to create an M-file.

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M-file building (step 1)

• “File” - “New” - “Script”

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M-file building (step 2)

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M-file building (step 3)• An simple example:

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Explanation of the example

• Line 1: instructs Matlab to delete all variables in the working directorydirectory.

• Line 2: instructs Matlab to clear the command window. Any text that now appears in the command window will be the result of running this M file not the result of previous activitiesrunning this M-file, not the result of previous activities.

• Line 3: blank lines help improve the readability of a M-file.

• Line 4 and 5: Assign values to A and B The semicolon prevents• Line 4 and 5: Assign values to A and B. The semicolon prevents Matlab from displaying the result in the command window; the percent sign begins the legible comment.

• Line 6: Intermediate results with suitable names sometimes• Line 6: Intermediate results with suitable names sometimes improve the legibility of the algorithm.

• Line 7: Invokes the built-in function sqrt() to compute the final lt

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result.

M-file saving (step 1)• “File” - “Save”

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M-file saving (step 2)• Type “hypo” as the file name, then click “Save”

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Run M-file (method 1)• Type the M-file’s name: “hypo” into command window and

then press the “enter” key.

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Run M-file (method 2: step 1)

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Run M-file (method 2: step 2)• Double click the file “hypo”;• Or single click the file “hypo” and single click “open”

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Run M-file (method 2: step 3)

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Run M-file (method 2: step 4)

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Summary of Lab 1

• Introduction to the LabIntroduction to the Lab

• Matlab overviewWh t i M tl b?– What is Matlab?

– Strengths and weaknesses of Matlab

• Basic manipulation in Matlab

– Start and quit Matlab

– The Matlab user interface

– M-file building, saving and running

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Next class

1 Vectors1. Vectors

2. Arrays

3 B il i f i3. Built-in functions

4. Some exercises

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