Date: Nov 21, 2012 2:39 PM
Author: Carlos Alejandro Perez Lasso
Subject: Optimization

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 with a Cost function that receives initial 3 parameters, reads experimental data, writes a file for parameter study in Abaqus, runs the simulation using the 3 parameters in the material model, reads the corresponding numerical result, compares it with the experimental data and returns a Cost Vector for the solver to do its job.
The problem: When running, the solver does 4 function calls in the 0 iteration and doesn't move from the initial 3 parameters. Thus no gradient is calculated and he thinks that the initial point is already a minimum. Here is what he says:

Norm of First-order
Iteration Func-count f(x) step optimality CG-iterations
0 4 246.506 0


Initial point is a local minimum.

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

"Optimization running.
Objective function value: 246.50561987942325
Initial point is a local minimum.

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

I would appreciate any help on this regard.

Thank you Matlab users.