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From: strefli3@gmail.com
Newsgroups: comp.soft-sys.matlab
Subject: Fmincon + Ansys, Looking for a global minimum
Date: 29 Nov 2006 15:08:46 -0800
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Hello,

I am attempting to use fmincon to optimize the cross sectional areas of
a 12 member 3-d truss. My design varaibles are the 12 radii and they
are subject to a lower and upper bound as well as a stress constraint
which happnes to be von-mises supplied my Ansys.

At the moment I can get the program to converge to a solution, but it
is a local minima, infact I can find several different local minima by
adjusting the initial guess; It is clear that this problem is not a
smooth one.

The program makes around 60 iterations with around 1600 function
evaluations before it convereges, updating the hessian almost every
time, if not twice. However, depending on the start location, the
convergance can be found in less iterations.

So my question is, if I know that all my constraints should be 0 (or
near 0) unless a variable is at it's lower bound, then shouldn't there
be some possibility to find the optimum solution based on the present
knowlege of the constraints?

I am open to try any global optimizers. If anyone knows an optimizer
that has the ability to take the contraints in as a seperate function,
please share.


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