MATLAB: What is the computational cost of an nargin check

computational costfor loopif statementMATLAB

I have a program that invokes a function a lot of times in a for loop. In that function I have to check the number of input arguments with an if statement. Does this remarkably influences the run-time? That specific function (which is invoked in the for loop) is a general purpose function so input check is needed.

Thank you, Zoli

Best Answer

Measure it: use either the profiler, or tic/toc . Make the loop do enough iterations to really create measurable times, and see what including/removing nargin does to the runing time.

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MATLAB: Nargin

nargin means "number of arguments in". In the above code it looks pretty useless:

if nargin < 2
  %do stuff
end

nargin in this case can only be 0 or 1, since yatzy(n) only allows for one input argument, (n), or no input arguments, yatzy. If you call yatzy with two input arguments, e.g.

yatzy(4,5)

It will error out with something along the lines of "Error using yatzy, more input arguments than expected"

Now as for future reference, since you're learning: nargin is typically used for error checking and so you can have optional arguments, e.g:

let's write a program f that takes one or two input arguments with the 2nd being optional:

function out = f(x,y);
if nargin==0
  %user called >>f
  error('Not enough input arguments, 1 is required');
elseif nargin==1
  %user called f(x)
  y = pi;
end  %if neither, user called f(x,y)

Here we've made sure the person enters at least one argument, x, if they entered a second one great! if not, the second one, y, = pi.

Good luck!

MATLAB: Array dimensions equivalence check

One alternative:

isequal(size(A), size(B)) || (isvector(A) && isvector(B) && numel(A) == numel(B))

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MATLAB: Nargin

MATLAB: Array dimensions equivalence check

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