Scripts and Functions

Copied from MATLAB Product Help

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M-files are basically text files with a .m extension which contain commands that MATLAB can read. Based on the way we use them, there are two types of M-files: scripts and functions.

M-file scripts

This is the simplest kind of M-file because they have no input or output arguments. They are useful for automating series of MATLAB commands, such as computations that you have to perform repeatedly from the command line. You can think that a script M-file is a text file with each line is a command you are going to enter in the Command Window.

Scripts share the base workspace with your interactive MATLAB session and with other scripts. They operate on existing data in the workspace, or they can create new data on which to operate. Any variables that scripts create remain in the workspace after the script finishes so you can use them for further computations. You should be aware, though, that running a script can unintentionally overwrite data stored in the base workspace by commands entered at the MATLAB command prompt.

Try entering the following commands in an M-file called mytestS.m:

x = 1:100;
xnumber = length(x);
totalx = sum(x);
average_x = totalx/xnumber

This file is now a MATLAB script. Typing mytestS at the MATLAB command line executes the statements in the script.

average_x =

   50.5000

M-file functions

Functions are program routines, usually implemented in M-files, that accept input arguments and return output arguments. You define MATLAB functions within a function M-file; that is, a file that begins with a line containing the function key word. You cannot define a function within a script M-file or at the MATLAB command line.

Functions always begin with a function definition line and end either with the first matching end statement, the occurrence of another function definition line, or the end of the M-file, whichever comes first. Using end to mark the end of a function definition is required only when the function being defined contains one or more nested functions.

Functions operate on variables within their own workspace. This workspace is separate from the base workspace; the workspace that you access at the MATLAB command prompt and in scripts. While using MATLAB, the only variables you can access are those in the calling context. The variables that you pass to a function must be in the calling context, and the function returns its output arguments to the calling workspace context.

Here's a simple M-file function that calculate the average of the elements in a vector:

function y = mytestF(x)
xnumber = length(x);
totalx = sum(x);
y = totalx/xnumber;

Try entering these commands in an M-file called mytestF.m. The mytestF function accepts a single input argument and returns a single output argument. To call the mytestF function, enter

x = 1:100;
mytestF(x)
ans =

   50.5000

Note that, there actually is a MATLAB internal function called mean which calculate the average of the elements in a vector.