Declare a Function in MATLAB: function Syntax, Files and Handles

Short answer: in MATLAB you declare a function with the lowercase keyword function on the first line of a function, followed by the output names, an equals sign, the function name and the input names in parentheses. Functions live in files, not at the command line, and the file name must match the name of the first function in the file. This page is for researchers and analysts who need to write their first reusable function, and it adds a comparison of the four places a function can live and a troubleshooting table for the errors that follow from getting that choice wrong.

What function declarations are used for in research

Analysis code tends to be repeated: the same cleaning step on every participant file, the same fit on every condition. Wrapping the step in a function gives it a name, defined inputs and outputs, and a single place to fix a bug. For the wider picture of what MATLAB is used for, see what MATLAB is used for.

Install or access (official source only)

MATLAB is a MathWorks product, so the install and the documentation both come from mathworks.com. Licence types and how an institution provides access are covered in MATLAB licensing. Nothing on this page depends on a particular toolbox: the function keyword is part of the base language.

How do I declare a function in MATLAB?

Create a new file whose name is the function name plus .m, and put the declaration on its first line. The keyword function is lowercase and required. The shape of the line depends on how many outputs you return:

Outputs	Declaration line
One output	function myOutput = myFunction(x)
Several outputs	function [one,two,three] = myFunction(x)
No outputs	function myFunction(x) (or function [] = myFunction(x))
No inputs	The parentheses are optional

The function name starts with a letter and can contain letters, digits and underscores.

Step by step: a worked example

1. Create a file named fact.m. The file name must match the first function in it.
2. On the first line write the declaration: function f = fact(n).
3. Add the body that assigns a value to the output f, then save the file in the current folder or on the MATLAB search path.
4. Call it from the command line or from another file: y = fact(5).

The MathWorks page on creating functions in files uses exactly this fact example.

Which kind of function should I use?

Most pages cover each kind separately. Side by side, the choice is mostly about where the function needs to be callable from.

Kind	Where it is defined	Available to	Notes
Function file (main function)	Its own .m file; the first function in the file	Anything on the path	File name must match the function name
Local function	After the main function in a function file, or inside a script	Only code in that same file	In scripts, each begins with function and ends with end
Nested function	Inside another function	Contained within its parent	Requires end
Anonymous function	One line, with @	Wherever the handle is passed	Single executable statement; see lambda (anonymous) functions in MATLAB

Can I define a function in a function?

Yes. A nested function is a function written entirely inside its parent function and it needs an end. The first function in a function file is the main function, and any later ones are local functions that only code in that file can call. An end is required for every function in a file if any function in it contains a nested function.

How do I call a function in a script?

Call it by name with its inputs, assigning the outputs you want: y = fact(5). The function file must be in the current folder or on the search path. A script itself is called by its file name, for example mystats.

Local functions in scripts and the R2024a change

Before R2024a, local functions in a script had to sit at the end of the file, after the last script code. From R2024a, they can appear anywhere in scripts and live scripts except inside conditionals or loops. A script file cannot have the same name as a function defined in it.

How do I declare a variable in MATLAB?

A variable is created by assigning to it. For functions, the input and output variable names are the ones you put on the declaration line. An optional arguments block after the line validates inputs, for example x (1,:) {mustBeNumeric, mustBeFinite}. If a call violates it, MATLAB throws an error such as “Invalid input argument at position 1. Value must be finite.” Put required arguments before optional ones. Loops that fill variables are covered in loops in MATLAB and conditions in if statements in MATLAB.

Function handles and anonymous functions

For a short expression you do not need a file. sqr = @(x) x.^2; creates a handle, and a = sqr(5) returns 25. An anonymous function holds a single executable statement. With no inputs, t = @() datestr(now); d = t() runs it, while omitting the parentheses returns the handle without running it. Values of variables used in the expression are captured when the handle is created and persist even if you clear the variables, so make a new handle to pick up new values. Handles can be stored in a cell array and called as f{3}(x,y), and can be saved with save and load. Avoid eval, evalin, assignin and load inside the body. Cell arrays are covered in cell arrays in MATLAB.

Output and how to read it

A function returns whatever has been assigned to its named outputs when it finishes. Leave the semicolon off a call to print the result, or assign it to a variable as in y = fact(5). To format printed output, see fprintf in MATLAB.

Troubleshooting

Symptom	Likely cause	Fix
Function not found when called	File not in the current folder or on the search path	Save it in the current folder or add its folder to the path
File name and first function name differ	File name differs from the first function name	Rename the file to match the first function
Cannot define a function at the command line	Functions are defined in files	Put it in a function file, a script, or use an anonymous function
Local function in a script errors	Placed before the end of the file in a release before R2024a, or inside a loop or conditional	Move it to the end of the script, or outside conditionals and loops in R2024a and later
Missing end problems	A nested function exists, but not every function ends with end	Close every function in the file with end
Script and function share a name	A script cannot have the same name as a function defined in it	Rename one of them

Free alternatives

Software	Type
GNU Octave	Free numerical computing environment
Python with NumPy and SciPy	Free general-purpose language with numerical libraries
Julia	Free programming language for numerical computing

Syntax differs between these tools, so the declarations above apply to MATLAB only.

FAQ

How do I declare a function?

Start a function file with function [outputs] = name(inputs), using the lowercase keyword, and save the file with the same name as the function.

Can I define a function in a function?

Yes, as a nested function that ends with end, or as a local function later in the same file.

How do I call a function in a script?

Write its name with arguments, such as y = fact(5), with the function file on the path.

How to declare a variable in MATLAB?

Assign a value to a name. Function inputs and outputs are named on the declaration line.

Sources (official docs)

• MathWorks, “Create Functions in Files”: https://www.mathworks.com/help/matlab/matlab_prog/create-functions-in-files.html (read 2026-11-07)
• MathWorks, “function” reference: https://www.mathworks.com/help/matlab/ref/function.html (read 2026-11-07)
• MathWorks, “Anonymous Functions”: https://www.mathworks.com/help/matlab/matlab_prog/anonymous-functions.html (read 2026-11-07)