How Do I Clear All Variables in MATLAB?

To clear all variables in MATLAB, you can use the commands clear or clearvars for the current workspace, and clear global or clearvars -global for global variables.

Understanding MATLAB Workspace

The MATLAB workspace is the memory space where variables are stored during a MATLAB session. When you create a variable (like x = 5;), it resides in the current workspace. As your programs run, the workspace can accumulate many variables.

Clearing Variables in the Current Workspace

The most common task is clearing variables from the current workspace. This is useful for starting fresh between different code snippets or analyses, ensuring that results aren't affected by variables left over from previous operations.

According to the reference: To clear all variables from the current workspace, use clear or clearvars.

Both commands achieve the same result when used without arguments to clear everything.

• clear: A fundamental command in MATLAB for removing variables, functions, and MEX-files from memory.
• clearvars: A more modern command, specifically designed for clearing variables. It offers more options for selectively clearing variables based on criteria like type or pattern, but when used alone, it clears all.

Examples

Here's how you use these commands:

% Create some variables
a = 10;
b = 'hello';
c = [1 2 3];

% View variables in the workspace (optional)
whos

% Clear all variables using clear
clear

% View workspace again (should be empty)
whos

Alternatively, using clearvars:

% Create some variables
x = 99;
y = magic(3);

% View variables
whos

% Clear all variables using clearvars
clearvars

% View workspace again
whos

Both clear and clearvars without any arguments effectively clear all variables from your current workspace.

Clearing Global Variables

MATLAB also supports global variables, which are accessible across different functions and scripts. Clearing these requires a specific command to avoid unintentionally affecting other parts of your application that might rely on them.

The reference states: To clear all global variables, use clear global or clearvars –global.

• clear global: Clears all variables that have been declared as global.
• clearvars -global: A clearvars specific option to clear only global variables.

Examples

Let's see how this works:

% Declare and assign a global variable
global myGlobalVar;
myGlobalVar = 123;

% Declare a regular variable
localvar = 456;

% View variables (myGlobalVar might not show with 'whos' directly
% unless within a function that declares it global, or you use 'whos global')
whos global % Shows global variables

% Clear only global variables
clear global

% View variables again (myGlobalVar should be gone, localvar remains if in current scope)
whos global
whos % localvar is still here if in the same scope

Using clearvars -global:

% Declare and assign a global variable
global anotherGlobal;
anotherGlobal = 'data';

% Clear only global variables using clearvars
clearvars -global

% View variables again
whos global % anotherGlobal should be gone

Summary Table

Here's a quick summary of the commands for clearing variables:

Best Practices

• Use clear or clearvars at the beginning of a script or function if you want to ensure it runs in a clean environment, free from previous variables.
• Be cautious when using clear or clearvars in larger projects, as you might inadvertently remove variables needed later in the code.
• Use clear global or clearvars -global with care, as global variables are often used to share data across multiple parts of a program. Clearing them might disrupt functionality elsewhere.
• To clear specific variables, you can list their names after clear or clearvars (e.g., clear var1 var2).

By using these commands, you can manage the MATLAB workspace effectively, keeping it tidy and preventing unwanted variable interference.