MATLAB Function

• This note focuses on user-defined functions.

In older MATLAB versions, every user-defined function had to live in its own .m file — a sign of how distinctive and central functions are in MATLAB. Modern MATLAB also allows non-function code together with one or more peer-level function definitions in the same .m file, but every function definition must come last: no non-function code may follow the end of a function definition.

Even so, the cleanest convention is to keep each function in its own same-named .m file. With that layout, no matter whether the function file is in the Current Folder or anywhere on the MATLAB search path, the function can be called by name from any other file or from the Command Window.

• When the name in the function declaration differs from the file name, the function can only be called externally via the file name.

To distinguish ordinary scripts from function files: a function definition must live in a .m file (and cannot be created in the Command Window), whereas a script is just a collection of statements that could equally be entered in the Command Window.

Definitions used below:

function file : a .m file that contains only function definitions

script file : a .m file that is not a function file

Basic Syntax

The basic syntax of a function definition is:

function output = myFunction(input)
% H1 comment
% Other comments
 
function_block
end

• The first line is the function declaration, specifying the function name and its input/output parameters
• The second line, the H1 comment, summarises what the function does; its content is searchable via lookfor
• Subsequent comment lines explain the function and are shown by help
• The keywords function and end mark the function’s beginning and end
  • In a standalone function file with no nested functions, end may be omitted

Matlab Functions Types

• For function-call resolution order, see Matlab Function Precedence Order.

Aside from the main function, functions fall into the following four categories:

1. Nested function
2. Local function
3. Private function
4. Anonymous function

Matlab Functions Arguments