MATLAB - Variables

MATLAB - Variables and Data Types

In MATLAB, a variable is a named storage location in memory. The fundamental principle is that every variable in MATLAB is an array, which can hold numbers, text, or more complex data. Even a single number is treated as a 1x1 array.

Creating and Assigning Variables

Assignment is done using the equals sign (=). MATLAB automatically determines the appropriate data type for the variable based on the value you assign.

% Assign a single numeric value (a 1x1 double array)
x = 16;

% The semicolon at the end suppresses output to the Command Window
% This is best practice for writing clean scripts.
y = sqrt(x);

% To see the value of y, simply type its name or use disp()
disp(y)

Output:

     4

If you execute an expression without assigning it to a variable, MATLAB stores the result in a temporary variable called ans.

% This calculation's result is stored in 'ans'
log(100)

% You can use 'ans' in the next calculation
result = ans * 5

Best Practices for Variable Naming

• Be Descriptive: Use names that describe the variable’s purpose, like initialVelocity or customerName instead of v or c.
• Start with a Letter: Variable names must start with a letter, followed by any combination of letters, numbers, and underscores.
• Case-Sensitive: MATLAB is case-sensitive, so myVar is different from myvar.
• Avoid Keywords: Do not use names of built-in functions or keywords (e.g., if, for, plot). You can check if a name is a function using exist('name').

Managing Workspace Variables

As you create variables, they populate the MATLAB workspace. You can manage them with these commands:

• who: Lists the names of all variables currently in the workspace.
• whos: Provides a detailed list, including variable name, size (dimensions), memory usage, and data type.
• clear: Removes variables from memory. clear varName removes a specific variable, while clear on its own removes all variables.

% Create a few variables
student_name = "Alex";
grades = [95, 88, 92];

% See what's in the workspace
whos

Expected Output:

  Name             Size            Bytes  Class     Attributes

  grades           1x3                24  double
  student_name     1x1               138  string

Common Data Types

While double (64-bit floating-point number) is the default, MATLAB supports many other data types:

• double: Default for numbers, e.g., x = 3.14.
• string: For text, enclosed in double quotes. Ideal for manipulating text data. E.g., s = "Hello, MATLAB!".
• char: For single characters or character arrays, in single quotes. E.g., c = 'H'.
• logical: Represents true (1) or false (0). E.g., isValid = true.
• cell: An array that can hold different data types in each element. E.g., C = {1, "text", [2 3]}.
• struct: A structure with named fields for organizing related data. E.g., patient.name = "John"; patient.age = 45;.

Creating Vectors and Matrices

Creating arrays is a core MATLAB skill. Here are the modern and most common methods.

Manual Creation

% A row vector (elements separated by commas or spaces)
row_vec = [1, 2, 3, 4, 5];

% A column vector (elements separated by semicolons)
col_vec = [1; 2; 3; 4; 5];

% A 2x3 matrix (semicolon starts a new row)
my_matrix = [1, 2, 3; 4, 5, 6];

Using Functions

% Create a vector of 10 evenly spaced points from 0 to 1
lin_vec = linspace(0, 1, 10);

% The colon operator: create a vector from 1 to 10 with a step of 2
colon_vec = 1:2:10; % Result: [1 3 5 7 9]

% Create a 3x4 matrix of all zeros
zero_mat = zeros(3, 4);

% Create a 2x2 identity matrix
ident_mat = eye(2);

Controlling Output Format

The format command controls how numbers are displayed in the Command Window. This does not change the stored value, only its appearance.

my_val = 100/3;

format short % Default, 4 decimal places
disp(my_val) % Displays 33.3333

format long % 15 decimal places for double
disp(my_val) % Displays 33.333333333333336

format bank % 2 decimal places
disp(my_val) % Displays 33.33

format rat % Closest rational fraction
disp(my_val) % Displays 100/3