lsqnonlin (lsqcurvefit , fmincon) does not change the variables in an optimization process to find the best fit

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Esi Tesi 2024-3-25

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https://ww2.mathworks.cn/matlabcentral/answers/2098706-lsqnonlin-lsqcurvefit-fmincon-does-not-change-the-variables-in-an-optimization-process-to-find-t

评论： Torsten 2024-4-2，9:57

I'm perfoming an optimization of parameters. The main difference between my work and a regular curvefiiting problem is that the function that should be fitted is one that obtains x-y data from a third party simulation software. Here is the main section of the code:

u_test = []; f_test = []; % Anything
x0 = [22,280]; 
force = @(x) sim_res(x,u_test,f_test) - f_test;
x = lsqnonlin(force,x0,[4,199],[40,350]);

and here is the function that goes into another software (ABAQUS) and obtains some simulation results (a set of x-y data):

function force = sim_res(x,u_test,f_test)
inp_initial(x(1),x(2)); % Replaces new coefficients for new iteration
pause(2) 
system('abaqus job=Al.inp user=NONLINEAR.for cpus=4 interactive' )
pause(2)
while exist('Al.lck','file')==2 % Some files have to be deleted
   pause(0.1) 
end
while exist('Al.odb','file')==0 % Some files have to be deleted 
   pause(0.1)
end 
[dis,force] = Read_ODB_outputs_node(); % Another function that obtains results
plot(dis,force,u_test,f_test)
% Some files have to be deleted 
delete('Al.prt'); 
delete('Al.com'); 
delete('Al.sim'); 
delete('Al.dat'); 
delete('Al.log');
end

The problem is that lsqnonlin does not change the initial values of x and after 2-3 iterations, the process stops and converges. The same happens with lsqcurvefit and fmincon. Can anyone find a solution for this?

Thanks in advance

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采纳的回答

Torsten 2024-3-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2098706-lsqnonlin-lsqcurvefit-fmincon-does-not-change-the-variables-in-an-optimization-process-to-find-t#answer_1430896

移动：Torsten 2024-3-25

We don't know if you get modified values for the array "force" from "ABAQUS" if the input vector "x" to "sim_res" is slightly changed by "lsqnonlin". If this is not the case, "lsqnonlin" will think that changing the parameters does not change the objective function and stops - usually with the message that the initial point is optimal.

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Esi Tesi 2024-4-2，9:52

I've tried these vaues (1e-6, 1e-3, 1e-2, 1e-1) for FiniteDifferenceStepSize and got the same result that after a few iterations, the solver gets stuck at some specific x value and iterates on them without any progress. Is there any option or parameter that controls this action?

Torsten 2024-4-2，9:57

I don't know the reason. Most probably, the values coming from ABAQUS are too inexact. This would cause that computing reliable derivatives with respect to the parameters being fitted fails.

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