Lecture Notes 3

Chapter 3: Introduction to MATLAB Programming

3.1 Overview of MATLAB Scripts

When multiple commands are needed for a final result, it is better to group them in a MATLAB script.
- Computer Program: A sequence of instructions that accomplishes a task.
- Execution: The computer follows the instructions sequentially.

3.2 MATLAB Scripts

A script is a sequence of MATLAB instructions stored in an .m file.
- Execution of a Script: Simply enter the name of the file (without the .m).
- File Naming Rules: Same as variable naming; must start with a letter, followed by letters, digits, or underscores.

3.3 Creating a Simple Script

Example: Create a script script1.m to calculate the area of a circle.
```
radius = 5;
area = pi * radius^2;
```
Viewing the Script:
- Open in the Editor Window or use the type command in the Command Window.

3.4 Documenting Scripts

Importance of Documentation: All scripts should be well-documented.
- Use % at the beginning of a line for comments.
- Example of documentation:
```
% This script calculates the area of a circle.
% First the radius is assigned
radius = 5;
area = pi * (radius^2);
```
- Help Command: Displays the first block of comments from the script.

3.5 Input and Output in MATLAB

Input Function:
- The simplest function is input(), which takes user input.
```
rad = input('Enter the radius: ');
```
- For string input, use 's' as a second argument.

3.6 Example Input Commands

Enter a vector or matrix:

v = input('Enter a vector:');
A = input('Enter a matrix:');

3.7 Output Functions

Output Functions: disp and fprintf.
- disp: Basic output without formatting.
```
disp('Hello');
```
- fprintf: Supports formatted output.
```
fprintf('The value is %d, for sure!
```

', 4^3);


### 3.8 Placeholders in Formatted Output
- Common placeholders:
- `%d`: integer 
- `%f`: float 
- `%c`: single character 
- `%s`: string
- **Example of Formatted Output:**
```matlab
fprintf('The int is %d and the char is %c
', 30, 'x');

3.9 Scripting with Input and Output

Example script sphereIO.m calculates volume:

radius = input('Please enter the radius: ');
volume = (4/3) * pi * radius^3;
fprintf('The volume is %.2f inches cube

', volume);


### 3.10 Plotting with MATLAB
- **Basic Plot:** Using `plot()` function.
- For multiple points, create vectors:
```matlab
x = 1:6;
y = [1 5 3 9 11 8];
plot(x,y);

3.11 Customizing Plots

Customizing colors, line types, and markers.
- Colors: r (red), g (green), b (blue), etc.
- Line types: - (solid), -- (dashed), : (dotted).

3.12 Working with Figure Windows

Commands to manage figure windows:
- clf: Clear current figure.
- figure(n): Create new figure or specify figure number.
- hold on/off: To retain plots.

3.13 File Input/Output

Modes of file operations: reading, writing, appending.
Writing Data: save command with -ascii qualifier.
Reading Data: Using load command for matrices.

3.14 Example of File I/O

Example of writing and loading data from a file.

save testfile.dat mymat -ascii;
mymat = load('testfile.dat');

3.15 User-Defined Functions

Function definitions include:
- function keyword, output argument, function name, input arguments, and body.

Example Function calcarea:

function area = calcarea(rad)
area = pi * rad^2;
end;