MATLAB: Help with Varargin

mathematicsnonlinearvarargin

I have a function called MySolve and i am looking to adapt it to use Varargin.
As far as i am aware Varargin allows defaults for parameters to be set. but can be over-ridden if an input is given. I am having trouble understanding the syntax for using Varargin, here is the function MySolve.m that i have written:
function [x,converged]=MySolve(f,x0,tol,maxit)
%Set Converged intial value to 0 (false)
%Set initial value of x as x0
converged=0;
x=x0;
%run a loop from 1 to maxit
for k=0:maxit
      x1=x;
      r=f(x);
      J=MyJacobian(f,x,1e-6);
      x=x-(J\r);
      if(max(abs(x-x1)))<tol && max(abs(f(x)))<tol
          converged=1;
      end
  end
I am looking to have defaults for tol and maxit as 1e-10 and 100 respectively.
any help is much appreciated.

Best Answer

I would suggest the following. This way, the input values are reflected. Hardwire the inputs you definitely want, and use varargin to hold the optional inputs.
function [x,converged]=MySolve(f,x0,varargin)
optargin = size(varargin,2);
if optargin == 0
    tol = 1e-10;
    maxit = 100;
elseif optargin == 1
    tol = varargin{1};
    maxit = 100;
else
    tol = varargin{1};
    maxit = varargin{2};
end
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