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Advanced MATLAB: Varargin and Nargin- variable inputs to a function 6

Posted by Doug Hull,

Most MATLAB functions are overloaded. That means that there are several ways to call them and that MATLAB will “Do The Right Thing” based on the number and types of inputs. As a simple example you can call SUM sum(M) %this will sum along the columns sum(M,2) %this will sum along the rows This video shows how you can implement the same behavior based on using VARARGIN: VARiable ARGuments IN NARGIN: Number ARGuments IN
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6 CommentsOldest to Newest

Markus replied on : 2 of 6


I sometimes use “exist” in order to realize variable inputs:

function bla(A,B,D)
if ~exist(‘D’, ‘var’)
D = 10; % default value

Here, I did not hard-code the order and number of input arguments. If I ever want to introduce an additional input C before D, like

function bla(A,B,C,D)

I do not have to change anything (except the function calls of course). I think both alternatives have their pros and cons.


Doug replied on : 3 of 6


You can use num2str to make a number into text. You can have a function output be string if that is what you want.


Luca Balbi replied on : 4 of 6

Hello Doug, great work as always!

I think that the recent introduction of the inputParser object has made things evolve a bit with respect to the nargin approach.
Have you ever thought about creating a video with a demo of inputParser?

dylan replied on : 5 of 6

i followed your code exactly and i get the following error:
>> main(1)
??? Undefined function or method ‘mtimes’ for input arguments of type ‘cell’.

Error in ==> main at 19
out=alpha * beta;

Jiro replied on : 6 of 6


Make sure you are using (curly) braces and not parentheses:

alpha = varargin{1}

“varargin” is a cell array, so you need to use braces to get the contents of each element. Parentheses will only give you back the element as a cell.

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