error in fitness function (gaoptimset) ??? despite convex function gaoptimset does not optimise 2010b

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Swarup 2014-5-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/130680-error-in-fitness-function-gaoptimset-despite-convex-function-gaoptimset-does-not-optimise-20

回答： Swarup 2014-5-23

采纳的回答： Alan Weiss

在 MATLAB Online 中打开

I have a single variable objective function. This variable goes into my for loop.

irrespective of what lower and upper bonds I assign; initial range i give and with vectorize option 'on'.

does not optimize. I get following values

x: 100.000000.
fval: 8231923.58.

My objective function does have a convex behavior. this plot was generated by manually setting the forloop upto 10000

And went I set the options = gaoptimset(options,'Vectorized', 'off');

??? Subscripted assignment dimension mismatch.
Error in ==> fcnvectorizer at 14
            y(i,:) = feval(fun,(pop(i,:)));
numberOfVariables = 1; % always 1
PopulationSize_input = 100; % can vary between 20 to 100
%%Bounds on our flowrate
lb =100; %100;
ub = 1000; %0.00050
%%---- parametarising Genetic algorithm-----------%%
options = gaoptimset;
% Modify options setting
%options = gaoptimset(options,'PopInitRange' ,[0 ; 0.00050]);
options = gaoptimset(options,'PopInitRange' ,[lb ; ub]);
options = gaoptimset(options,'MutationFcn' ,@mutationadaptfeasible);
options = gaoptimset(options,'CrossoverFcn' ,@crossoverarithmetic);
options = gaoptimset(options,'PopulationSize', PopulationSize_input);
options = gaoptimset(options,'Display', 'off');
options = gaoptimset(options,'PlotFcns', {  @gaplotbestf @gaplotbestindiv @gaplotrange @gaplotselection });
options = gaoptimset(options,'Vectorized', 'off');
options = gaoptimset(options,'UseParallel', 'never');
%options = gaoptimset(options,'HybridFcn' ,@fminsearch);
%options = gaoptimset('OutputFcns', @gaoutputgen);
%options = gaoptimset(options,'OutputFcns' ,{ @gaplotbestf @gaplotbestindiv @gaplotrange @gaplotselection });
FitFcnn = @(f) HydraulicCOAX(f);
    [x, fval] = ga(FitFcnn,numberOfVariables,[],[],[],[],lb,ub,[],options);
      fprintf('The flow rate: %6.6f.\n',x);
      fprintf('The Qeng: %6.2f.\n',fval);

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Matt J 2014-5-23

What happens when you use a different optimizer, e.g., fminsearch?

Swarup 2014-5-23

在 MATLAB Online 中打开

Hi Matt,

1) I tried using fminsearch as options = gaoptimset(options,'HybridFcn' ,@fminsearch);

??? Undefined function or variable "Q".

Error in ==> HydraulicCOAXfmin at 54 q=size(Q,2);

Error in ==> @(f)HydraulicCOAXfmin(f)

Error in ==> validate>@(x)fitness(x,FitnessFcnArgs{:}) at 136 fitness = @(x) fitness(x,FitnessFcnArgs{:});

and fminsearch

Optimization running. Error running optimization. Subscripted assignment dimension mismatch.

*****************************************

Is it because the for loop in my objective function takes integer values??

and the f (which come from PopulationSize =100) are not integers.

function [Peng] = HydraulicCOAXfmin(f)

for i=1:f

Q(i)= f/10/3600

rho=999.702;

eta=1305.875E-6;

vi(i)=Q(i)/((rii^2)*pi);

...

end

q=size(Q,2)

for j=1:q %Rückskalieren auf m^3/h für plot

Q(j)=Q(j)*3600;

end

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Answer 1

Alan Weiss 2014-5-23

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/130680-error-in-fitness-function-gaoptimset-despite-convex-function-gaoptimset-does-not-optimise-20#answer_137978

I don't know why you think that the solver failed. From your graph, the minimum value of your objective function occurs at the point x = 0, and rises in a convex fashion as x increases. So you give a lower bound of 100 and an upper bound of 1000, and of course you find that the best point in this range is at x = 100.

It looks to me as if the solver is doing its job.

However, I am not at all sure why you are using ga on this type of function. For a smooth function, use an Optimization Toolbox solver such as fmincon.

Alan Weiss

MATLAB mathematical toolbox documentation