fzero - how to set maximum number of iterations

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Alessandro D
Alessandro D on 9 Jul 2018
Commented: Alessandro D on 9 Jul 2018
Dear users, I am using fzero to find the root of a nonlinear function. I call the routine as
x = fzero(fun,x0,options)
and I set options as
options = optimset('TolX',1e-6);
However I would like to set the maximum number of iterations as well, but it seems it's not possible, at least according to the documentation. If someone has a suggestion, please let me know! Thanks

Accepted Answer

dpb on 9 Jul 2018
"Yes, we have no bananas today!"
fzero doesn't use the iteration count variables in the options object, true.
If it were important-enough to you, you could write an output function and have it count the times it was called and return the stop flag variable as true when a desired number of iterations reached. The internal counter would have to be made persistent, of course, to retain the count between calls.
I've never tried such a thing but seems at least theoretically possible altho begs the question of "why?" would you need it...
  1 Comment
Alessandro D
Alessandro D on 9 Jul 2018
In general it is always a good idea to have a stopping rule also on the number of iterations, otherwise the algorithm could go on forever :)
In my specific problem, convergence is not guaranteed so I wanna stop the algorithm after a given number of iterations. I will implement your suggestion then. Even though I am considering writing my own bisection routine (it could be simpler). In the end fzero is just a fancier bisection based on Brent method

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