matlab practice 1 introducing matlab lecture notes on video search & mining, spring 2012...

MATLAB Practice 1Introducing MATLAB

Lecture Notes on Video Search & Mining, Spring 2012

Presented by Jun Hee Yoo

Biointelligence Laboratory

School of Computer Science and Engineering

Seoul National Univertisy

http://bi.snu.ac.kr

© 2012, SNU CSE Biointelligence Lab., http://bi.snu.ac.kr 2

Contents

What is the MATLAB? Pros & cons. Environment

Basics Variables Operators Editor Loop, Branch Practice I

To be Beginner (maybe next time) Functions Error Handling Useful Tips


What is MATLAB?

MATLAB Practice 1 - Introducing MATLAB


What is MATLAB?

Short for MATrix LABoratory Pros

Ease to Use A lots of built-in useful functions. Script language

Platform Independence Can use with C/C++ and JAVA

Cons Slower than native programs It’s commercial software

GNU Octave is free!!!

www.mathworks.com

http://www.mathworks.com/


Environment

Base window

Browser

Workspace

CommandWindow

CommandHistory

Detail(Preview)

StartButton


Environment

Figure window Plot Tool

logo.m


Environment

Text Editor Window


Basics



Basics

Variables

Basic classes(type) Integer(int8, int16, int32, int64, uint8, uint16, uint32, uint64) Real

Single Double x = 10 Complex x = 10 + 9i

Character x = ‘a’ ( to assign string, ‘abc’ or [‘a’ ‘b’ ‘c’] )

And Etc. (cell, struct, object, boolean) What is different between ‘x = 10’ and ‘x = 10;’?

variable = expression(Double is default type)


Basics

Assign matrix 1 Dim

2 Dim

3 Dim

x1 = [1 2 3];x2 = [1, 2, 3];x3 = [1;2;3];

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

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

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

x = [1 2 3; 4 5 6; 7 8 9];x( :, :, 2) = [10 11 12; 13 14 15; 16 17 18];


Basics

Assign matrix DIY

- Create Dim 4 and Dim 5 matrix.

x = [1 2 3; 4 5 6; 7 8 9]; - 2Dx( :, :, 2) = x( :, : ); - 3Dx( :, :, :, 2) = x( :, :, :); - 4Dx( :, :, :, :, 2) = x( :, :, :, : ); - 5D


Basics

Assign Matrix Elements A = [ 1 2 3; 4 5 6 ]; How to change matrix A to ?

Using subscript To Access , A(1, 3);


Basics

Usage of ‘:’ in subscript DIY

>> A = [ 1 2 3; 4 5 6; 7 8 9 ]; >> A( :, 2 ); >> A( 1, : ); >> B = A; >> B( :, :, 2 ) = 2*A; >> B( 1, 1, : ); >> B( :, :, 3) = 3*A;


3 6 9

12 15 18

21 24 27

Basics

Usage of ‘:’ in subscript DIY

2 4 6

8 10 12

14 16 18

1 2 3

4 5 6

7 8 9

𝐵 (1 ,: ,: )=[1 2 32 4 63 6 9]

𝐵 (2 ,: ,: )=[ 4 5 68 10 1212 15 18]

B =

Try other cases!


Basics

Dimension and index

2D

3D


Basics

Basic operators

Operation Algebraic Form MATLAB form

Addition a + b

Subtraction a – b

Multiplication a * b

Division a / b

Exponentiation a ^ b

< Arithmetic Operations between two scalars >


Basics

Basic operators

Operation MATLAB form Comments

Matrix Addition A + B A and B must be same dimension.

Matrix Subtraction A – B A and B must be same dimension.

Matrix Multiplication A * B cols of A and rows of B must be same.

Matrix Right Division A / B ?

Matrix Left Division A \ B ?

< Common Matrix Operations >


Basics

Basic operators DIY

>> A = [ 1 2 3 ]; >> B = [ 2 3 4 ]; >> A / B ans = ?

DIY >> A = magic(3); >> B = [ 1; 2; 3 ]; >> x = A \ B >> A*x ans = ?

In MATLAB, if matrix is not square shape or doesn’t have inverse matrix,it uses ‘pseudo inverse matrix’.


Basics

dot operator DIY

>> A = pascal(3); >> B = A ^ 2; % this is same as B = A * A; >> C = A .^ 2;

B and C are same?

DIY >> A = [ 1 2 3 ]; >> B = [ 2 4 8 ]; >> A .* B % in this case, A and B must be same

% shape


Basics

dot operator A .* B

Element-by-element multiplication of a and b. Both ar-rays must be the same shape, or one of them must be a scalar

A ./ B Element-by-element right division of a and b : a(i,j) /

b(i,j). Both arrays must be the same shape, or one of them must be a scalar.

A .\ B Same constraints as A ./ B.


Basics

colon operator DIY

A = 1:10; B = 1:2:10; C = 5:0.5:7; D = 0:-1:5;

A = [ 1 2 3 4 5 6 7 8 9 ] B = [ 1 3 5 7 9 ] C = [ 5.0000 5.5000 6.0000 6.5000 7.0000 ] D = [ 0 -1 -2 -3 -4 -5 ]


Basics

Transpose operator DIY

>> A = [ 1 2 3 ]; >> B = A’ >> C = A’’


Basics

Relational & Logical Operators

Operator Operation Operator Operation

== Equal to & AND

~= Not Equal to | OR

> Greater than ~ NOT

>= Greater than or equal to

< Less than

<= Less than or equal to


Basics

Relational & Logical Operators DIY

>> x = [ 0 : 3 : 15 ]; >> y = [ 0 : 2 : 10 ]; >> x > y >> x == y >> x < y >> x ~= y >> u = randint(1, 6); >> v = randint(1, 6); >> u & v >> u | v >> ~u


Basics

Tips clear variable_name

remove variable from workspace ‘clear all’ will remove all variables in workspace

clc clear command window


Basics

*.m file Using command windows is inefficient when process

long code. So, MATLAB supports a script editor

Click or CTRL+N


Basics

Editor

1. new document 2. execute current m-file

Do not use any white space character in file name. Please, write your file name in English.

Also, the path should be written in English.

1 2


Basics

Loop ‘for’ statement

for iteration = initial_value : step : final_value

end

DIY ( write in the script editor )

for i = 1:10

disp(i);

end

*while is loop statements too.


Basics

Branch ‘if’ statement

if relation or logical expression

statements;

elseif relation or logical expression % optional

statements;

else % optional

statements;

end

* keyword ‘swicth’ is branch statement too.


Basics Loop and Branch statements can be nested

Examplefor i = 1:2:10 if i <= 5 if i == 1 disp(i); end elseif i > 5 && i < 10 for j = i:10 disp(j); end else endend


Practice I



Practice I

Function call MATLAB has many powerful Built-in functions. DIY

>> A = rand(1); >> B = ceil(A);

To see the explanation of functions >> help function_name

DIY >> help rand


Practice I

Automated Lottery Program Generate 6 number between 1~45 for n times (n = 100) Generated numbers must not contain same number.

You can use… ceil() rand() sum() Google!!

You can not use… Any other random functions. (such as randperm())

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