Checking your Ins and Outs: The underused MATLAB Input Parser

Did you know that MATLAB has a built-in function for managing and validating inputs?

The MATLAB Input Parser allows you to validate inputs for accuracy and assign defaults to make your code easier to maintain. Let’s jump in:

I am working on a new function to generate cross-frequency coupling relationships within an EEG data structure. In this case, I first define my function and my input. I want the user to input an EEGLAB EEG SET structure and some other parameters that I will define as I write the function. We specify the “other inputs” to MATLAB using the varargin command.

function mvar = fx_gedcfc_base( EEG, varargin )

Next, we will create an inputParser object which we will call p.

function mvar = fx_gedcfc_base( EEG, varargin )
   p = inputParser;

At this point, we now begin to use the inputParser for common tasks that usually would take many more lines of code to add manually.

  1. Let’s make EEG a required input and make sure it is a structure:


  1. Let’s also check for a phase or amplitude optional value that can act as a parameter. If a user does not supply a ‘phase’ or ‘amplitude’ then set default values:
function mvar = fx_gedcfc_base( EEG, varargin)

    defaultPhase = 10;
    defaultAmplitude = 30;
    ip = inputParser;
    addOptional(ip,'phase',defaultPhase, @isinteger);
    addOptional(ip,'amplitude',defaultAmplitude, @isinteger);
    fprintf('fx_gedcfc_base function: Phase %d, Amplitude %d\n', ip.Results.phase, ip.Results.amplitude);

    mvar = EEG;

Here is our completed function. When we call it from our test file the output from: mvar = fx_gedcfc_base(EEG);

>> mvar = fx_gedcfc_base(EEG);
fx_gedcfc_base function: Phase 10, Amplitude 30

That’s it for the basic use of inputParser. The class itself is much more powerful and has many uses.

Ernest Pedapati, M.D., M.S.
Ernest Pedapati, M.D., M.S.
Associate Professor of Psychiatry

Physician and Neuroscientist interested in neurodevelopmental conditions.