FMINCON - Failure in initial objective function evaluation. FMINCON cannot continue

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I am trying to solve a bar optimization problem, passing the initial conditions (the area of each bar) and all variables as a struct but I am facing the following problem:
"Failure in initial objective function evaluation. FMINCON cannot continue."
fem = struct(...
'x',x0,... % Initial set of points
'NODE',NODE,... % [NNode x 2] array of nodes
'ELEM',ELEM,... % [NElem x 2] array of elements
'v',{v},... % Cell defining the variables
'NNode',size(NODE,1),... % Number of nodes
'NElem',size(ELEM,1),... % Number of elements
'NVar',size(v,1)... % Number of variables
);
Plot10bar(fem);
mass = GetMass10bar(fem);
fprintf('Initial Mass = %f\n',mass);
[x,fval,exitflag,output,lambda,grad,hessian] = ...
fmincon(@GetMass10bar,x0,[],[],[],[],lb,ub,@GetConstraints10bar,options);
mass = GetMass10bar(fem);
fprintf('Final Mass = %f\n',mass);
Plot10bar(fem);
Thank you,
André Leitão
  2 Comments
AXL
AXL on 11 Nov 2017
GetMass10bar evaluates the mass of 10-bar-truss! If I want to evaluate the initial mass, before the optimization process happens, I have to use, as argument of this function, the struct fem, which contains cross-section areas and nodal coordinates (used in to optimized the truss).

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Accepted Answer

AXL
AXL on 11 Nov 2017
I solved it using this:
[x,fval,exitflag,output,lambda,grad,hessian] = ...
fmincon(@GetMass18bar,x0,[],[],[],[],lb,ub,...
@GetConstraints18bar,options,fem);

More Answers (1)

Walter Roberson
Walter Roberson on 6 Oct 2017
You assign a struct to fem and then you call
mass = GetMass10bar(fem);
this suggests that the function GetMass10bar normally expects to be passed a single parameter that is a struct.
You then have
[x,fval,exitflag,output,lambda,grad,hessian] = ...
fmincon(@GetMass10bar,x0,[],[],[],[],lb,ub,@GetConstraints10bar,options);
fmincon passes a numeric vector with the same number of elements as x0; it does not pass a struct.
If your code for GetMass10bar cannot handle either a struct or a numeric vector, then the fmincon call to GetMass10bar is going to fail.
GetMass10bar appears to be your own code; I do not find any reference to it anywhere on the Internet.
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