Matlab M File

An M file is a plain-text file with the .m extension that MATLAB executes. There are two kinds—script files and function files—distinguished only by the file’s first non-comment line.

Script File

A script is a sequence of statements that runs in the base workspace, just as if the lines had been typed into the Command Window in order.

• No function declaration at the top
• Reads and writes the base workspace directly (no separate workspace of its own)
• Modern MATLAB allows local function definitions at the end of a script; they are visible only to the script

% myScript.m
x = 1:10;
y = x.^2;
plot(x, y)

Function File

A function file’s first executable line is a function declaration. Each call gets its own function workspace that is isolated from the base workspace.

• The file name should match the (main) function name; if it does not, callers from outside the file must use the file name
• A function file may also contain local functions and nested functions; only the main function is visible from outside
• See Matlab Functions Types for the full taxonomy

% mySum.m
function s = mySum(a, b)
s = a + b;
end

Discovery and the Search Path

MATLAB locates an M file by searching, in order, the Current Folder and then every directory on the MATLAB search path. The first match wins; resolution within a single folder follows Matlab Function Precedence Order.

• View the path with path; add a folder with addpath; persist the change with savepath
• A folder named private has restricted visibility—see Private Function
• A folder whose name starts with + defines a package; one whose name starts with @ defines a class

Other M-Family Files

• .mlx — Live Script: same idea as a .m script but with rich text and inline output. Edited in the Live Editor; can be exported to .m.
• .p — P-code: an obfuscated, executable form of a .m file
• .mex* — compiled C/C++/Fortran extensions, with a platform-specific suffix