# 5.4.1: Function Names and MATLAB Keywords

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$ $$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$$$\newcommand{\AA}{\unicode[.8,0]{x212B}}$$

User defined MATLAB function names follow the same rules as variable names:

It may have numbers and/or an underscore "_"

It cannot have a space, a hyphen, parentheses, a period, nor another symbol.

The function filename and the name on the function declaration line (a.k.a. signature) inside the file should be the same. See this link: https://www.mathworks.com/help/matlab/ref/function.html

Do not give a user-defined function the same name as a built-in function. That causes a "name collision". You can check the name like this:

which sum % MATLAB will tell you that this is a built-in function and will display the path to the library which contains this function.

which my_super_function % MATLAB will tell you that this function is "not found", so it is OK to use as a function name.

If you give your function the name of a built-in function, you can undo this by renaming your function, then enter this command:

clear functions

MATLAB has keywords that are reserved for its own use.
You cannot use these words as names of variables or functions.
Entering "iskeyword" gives a list of MATLAB's keywords in alphabetical order:

'break'
'case'
'catch'
'classdef'
'continue'
'else'
'elseif'
'end'
'for'
'function'
'global'
'if'
'otherwise'
'parfor'
'persistent'
'return'
'spmd'
'switch'
'try'
'while'

This video gives a clear explanation of defining a MATLAB function:

Section 10.2 reminds us not to create a variable nor a our own function with the same name as a MATLAB function.

That is, don't create a variable nor a function with a name such as sin, sqrt,

This page titled 5.4.1: Function Names and MATLAB Keywords is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Carey Smith.