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Subject: Re: Optimization
Date: Wed, 21 Nov 2012 22:18:10 +0000 (UTC)
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"Carlos Alejandro Perez Lasso" <carlosalejandro85@gmail.com> wrote in message <k8jaks$fqr$1@newscl01ah.mathworks.com>...
> Hi Matlab users,
> 
> My purpose is to use the Optimtool to estimate material model parameters so that running the model with such parameters in Abaqus results in a predicted curve close to some experimental data. 
> I am trying to solve the problem with the lsqnonlin solver 
============

If it's a curve fitting problem, mightn't it be better to use lsqcurvefit.


> Optimization completed because the size of the gradient at the initial point 
> is less than the default value of the function tolerance.
==========

This usually occurs because you have quantizing operations like ROUND, FLOOR, CEIL, etc... in your objective function. They make the function locally flat in places, making the initial point trivially a point of zero gradient.