How to Fix Undefined Function Error in MATLAB Quickly

The undefined function error in MATLAB happens when MATLAB cannot find the function you are trying to use. To fix it, ensure the function file is in the current folder or on the MATLAB path, and check for any spelling mistakes in the function name.

Why This Happens

This error occurs because MATLAB cannot locate the function you want to run. It might be missing from your current folder or not added to MATLAB's search path. Sometimes, a typo in the function name causes MATLAB to look for a function that does not exist.

matlab

result = myFunction(5);

Output

Error using myFunction
Undefined function or variable 'myFunction'.

The Fix

To fix this, first check that the function file myFunction.m exists in your current folder or in a folder added to the MATLAB path. You can add a folder to the path using addpath('folder_path'). Also, verify the function name is spelled correctly in your code.

matlab

% Suppose myFunction.m contains:
function y = myFunction(x)
    y = x^2;
end

% Call the function after ensuring it is on the path or in the current folder
result = myFunction(5);

Output

result =
    25

Prevention

Always keep your function files organized in known folders and add those folders to the MATLAB path at the start of your session. Use MATLAB's which command to check if MATLAB can find your function. Avoid typos by copying function names or using autocomplete features in the editor.

Related Errors

Other similar errors include Undefined variable when a variable is not defined before use, and Function not found when a toolbox function is missing because the toolbox is not installed or licensed. For toolbox functions, check your installed toolboxes with ver.

Key Takeaways

Ensure the function file is in the current folder or on the MATLAB path.

Check for spelling mistakes in the function name before calling it.

Use addpath to include folders containing your functions.

Use which functionName to verify MATLAB can find your function.

Keep your functions organized and use MATLAB editor autocomplete to avoid typos.