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what are the scaling factors of Optimization objective and constraint functions ?

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Old   May 1, 2014, 09:51
Default what are the scaling factors of Optimization objective and constraint functions ?
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Hi all
please let me know why the objective and constraint functions are multiplied by the 0.001 ?

Best Regards

% Optimization objective function with scaling factor
% ex= Objective * Scale
OPT_OBJECTIVE= DRAG * 0.001
%
% Optimization constraint functions with scaling factors, separated by semicolons
% ex= (Objective = Value ) * Scale, use '>','<','='
OPT_CONSTRAINT= ( MAX_THICKNESS > 0.04 ) * 0.001
%
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Old   May 15, 2014, 16:16
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Sean R. Copeland
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Hello mechy,

For the optimal design problems, SU2 uses the scipy optimization libraries. There is an initial step that the optimizer takes to perturb the design in its search for the local optimum. We generally scale the objective function to control the size of this initial step to ensure it is not too large. For different objective functions, the value of this scaling factor needs to be adjusted -- in general there's no set of guidelines to select the value, it just takes a little experimentation.



-Sean
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Old   January 27, 2015, 09:37
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Zeno Belligoli
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Dear Sean,

it happened to me that if I set the scaling factor to a small number ( e.g. OPT_OBJECTIVE=DRAG*0.001) and I start an optimization with already a solution_flow.dat and a solution_adj_cd.dat, the optimization stops at the end of DSN_001 with the following message:

done
./DESIGNS/DSN_001
./DESIGNS/DSN_001
Optimization terminated successfully. (Exit mode 0)
Current function value: 0.0003926472324
Iterations: 1
Function evaluations: 1
Gradient evaluations: 1

Where the current function value corresponds exactly to the value of the objective function at the end of the direct simulation multiplied by the scaling factor 0.001. Whereas if the scale is increase to 0.1, or 0.01, the optimization works but it produces negative volume cells at later stages (around DSN_006) and the FGMRES solver diverges.

Any hint here?

Thanks,

Z
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