From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Optimization
Date: Wed, 21 Nov 2012 22:18:10 +0000 (UTC)
Organization: Xoran Technologies
Lines: 15
Message-ID: <k8jjv2$ioc$>
References: <k8jaks$fqr$>
Reply-To: <HIDDEN>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Trace: 1353536290 19212 (21 Nov 2012 22:18:10 GMT)
NNTP-Posting-Date: Wed, 21 Nov 2012 22:18:10 +0000 (UTC)
X-Newsreader: MATLAB Central Newsreader 1440443
Xref: comp.soft-sys.matlab:783236

"Carlos Alejandro Perez Lasso" <> wrote in message <k8jaks$fqr$>...
> 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.