Doug's MATLAB Video Tutorials

January 8th, 2008

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

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

Find the files here. PodCast here Other videos have been gathered here: http://blogs.mathworks.com/pick/category/video/ Other Advanced MATLAB posts have been gathered here: http://blogs.mathworks.com/pick/category/advanced-matlab/

By Doug Hull

Doug first used MATLAB in 1994, could not figure it out until he got some help in 1995. He is now dedicated to making sure that no one else wastes a year of their life not knowing MATLAB like he did.

13:47 UTC | Posted in Format: PodCast, Format: Video, Level: Advanced | Permalink | 6 Comments »

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

Justin replied on January 8th, 2008 at 14:32 UTC :

Can your output ever be a text and not a number?
Markus replied on January 9th, 2008 at 11:59 UTC :

Hi!

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

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

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.

Regards
Markus
Doug replied on January 9th, 2008 at 12:26 UTC :

Justin,

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

Doug
Luca Balbi replied on January 11th, 2008 at 01:59 UTC :

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 March 28th, 2008 at 22:27 UTC :

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 March 29th, 2008 at 08:39 UTC :

dylan,

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.