1.5 - Getting Started with MATLAB

What is MATLAB?

• Creator: Cleve Moler, a scientific computing expert
• Primary Purpose: Highly suitable for scientific computing applications/tasks
• General Purpose: Can be used for general-purpose applications, but not as effective
• Alternative Languages**: For non-scientific computing tasks, better to use C++, Java, Python, etc.

Key Features

Performance

• JIT Compilation: From R2015a onwards, uses Just-In-Time (JIT) compilation
  • First time a function/script is called → code compiled into machine instructions and stored
  • Subsequent calls to same function/script → very fast execution

Built-in Functions

• Optimization: Fully compiled and heavily optimized built-in functions
• Multithreading: Many functions are multithreaded
• Special Instructions: Many exploit special machine instructions for efficiency
• Algorithm Selection: Some choose among different algorithms for most suitable approach
• Numerical Accuracy: All implemented to prevent unnecessary numerical error
• Examples: Functions for solving linear systems, fitting functions to data points, optimizations

Comparison with Other Languages

• Difficulty: Very difficult and time-consuming to implement equivalent scientific computing programs in C/C++, Java, or other general-purpose languages
• Performance: Hard to match MATLAB's speed and accuracy for scientific tasks

Command Window

• Function: Works like command line in Python
• Execution: Statement executed immediately when you press Enter
• Prompt: >>
• Main Usage:
  • Call scripts for applications
  • Perform simple computations with series of statements

Variables

Basic Usage

• Declaration: Variables can be used without declaration
• Type Selection: MATLAB automatically chooses appropriate types
• Case Sensitivity: Variable names are case-sensitive
• Example:

>> a = 4    % Creates variable a with value 4
>> A = 5    % Different from variable a

Special Variables

•  ans: Stores last output if no variable specified for result

>> 1+1
ans = 2
>> ans+4
ans = 6

Text Handling

Character Arrays vs String Arrays

• Character Arrays: Use apostrophes 'text'
  • Mainly for short pieces of text (shorter overhead) • String Arrays: Use quotation marks "text"
  • Come with many functions for working with text as data

Examples

>> s = 'This is a character array'
>> st = "This is a string array"

Output Control

Suppressing Output

• Method: End statements with semicolon (;)
• Example:

>> s = 'Where is the output?';  % No output displayed

Formatting Output

• format compact: Compact display
• format long: Long decimal display
• Example:

>> format compact
>> a = 2.12345    % Shows: 2.1235
>> format long
>> a              % Shows: 2.123450000000000

Vectors and Matrices

Creation

• Matrix Syntax: Use square brackets [ ]
• Row Separation: Use semicolon ;
• Column Separation: Use space or comma
• Examples:

>> A = [1 2; 3 4]          % 2x2 matrix
>> b = [-1; 0]             % Column vector
>> D = [-3,2,1; 1,0,-2]    % 2x3 matrix

Matrix Information

• size(): Get matrix dimensions

>> size(D)     % Returns [2 3]
>> size(D, 1)  % Returns 2 (rows)
>> size(D, 2)  % Returns 3 (columns)

Transpose

• Operator: Use apostrophe '
• Example:

>> D'  % Transposes matrix D

Range Creation (Colons)

Basic Syntax

• start:end: Creates sequence from start to end
• start:step:end: Creates sequence with specified step
• Examples:

>> t = 1:6        % [1 2 3 4 5 6]
>> t = 2:2:8      % [2 4 6 8]
>> t = 10:-1:2    % [10 9 8 7 6 5 4 3 2]

Matrix Operations

Basic Operations

• Addition/Subtraction: Element-wise with same dimensions
• Multiplication: Standard matrix multiplication rules apply
• Example:

>> A = [1 2; 3 4];
>> B = [-1 -3; -4 0];
>> A + B          % Element-wise addition
>> A * C          % Matrix multiplication (if dimensions compatible)

Matrix Indexing

Key Points

• Starting Index: First index is 1, not 0
• Syntax: Use parentheses (row, column)

Indexing Examples

>> C = [1 2 3 4 5; 6 7 8 9 10; 11 12 13 14 15];
>> C(2,3)           % Returns 8
>> C(1,:)           % Returns entire first row
>> C(:,2)           % Returns entire second column
>> C(1:2,:)         % Returns first two rows
>> C([1 3], [4 2])  % Returns specific elements
>> C(2, 3:end)      % From column 3 to end of row 2

Assignment

• Modify Elements: Can assign to specific indices

>> C(2,:) = [-1 -2 -3 -4 -5]  % Replace entire row
>> C(:,2) = [-9; 0; 3]        % Replace entire column

Character Array Indexing

ไม่ใช่ String Array นะ if so, we need special method!

• Same Rules: Character arrays follow same indexing rules

>> s = 'Hello, Thailand';
>> s(3:6)  % Returns 'llo,'

Scripts

Purpose and Usage

• Function: Execute many statements in sequence (like running a normal program)
• File Extension: Save as .m files
• Execution: Use filename to run

Example

• File: Save to ex1.m

a = 4;
b = 2;
c = a+b;
d = c*3 - a

• Run: Type ex1 in command window

Text Display

disp() Function

• Purpose: Display text output
• Apostrophe in Text: Use double apostrophes '' to display single apostrophe
• Example:

>> disp('What''s up!');  % Displays: What's up!

Control Structures

For Loops

• Range Syntax:

for i = 2:6
    i
end

• Array Syntax:

for j = [3 8 -1 4]
    j
end

While Loops

• Syntax:

i = 2;
while i ~= 5
    i = i+1
end

• ~ (Tilde) ก็คือ not นั่นแหละ

If Statements

• Full Syntax:

if condition
    % code
elseif condition
    % code
else
    % code
end

Functions

Basic Function Structure

• File Requirement: Filename must match function name • Syntax:

function output = functionName(input)
    % function body
end

Simple Function Example

• File: Save to mult2.m

function v = mult2(x)
    v = x*2;
end

ต้องตั้งชื่อ file ให้เหมือนชื่อ function ด้วยนะ แล้วถ้ามีหลาย function ในไฟล์เดียว มันจะ access ได้ function main (ก็น่าจะเป็นชื่อ file) จากนอก file ได้เท่านั้น!!

Multiple Inputs/Outputs

• Syntax:

function [u, v] = foo1(x, y, z)
    u = x+y;
    v = x*z;
end

• Calling:

>> [a, b] = foo1(2, 3, 4)  % a=5, b=8

Recursion

• Allowed: MATLAB supports recursive functions
• Example: Fibonacci function

function v = fib(n)
    if n < 0
        error('Invalid input');
    elseif n <= 1
        v = n;
    else
        v = fib(n-1) + fib(n-2);
    end
end

Comments and Help

Comments

• Syntax: Use % for comments

>> x = 2; % This is a comment

Getting Help

• Commands:
  • help functionName - Basic help
  • doc functionName - Full documentation
  • help * - List all functions
• Examples:

>> help switch
>> doc switch