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setting up the ''options' in fmincon

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ektor on 29 Dec 2017
Commented: Star Strider on 29 Dec 2017
Dear all,
I want to maximize a function, where the univariate unknown, x, with respect to which the maximization takes place is bound between -1 and 1. This is the only constraint. So, I use this
[],[],[],[],-1,1,[], options);
The function is complicated which means that I can not solve the gradient or Hessian anallytically
However, I am not sure how to set up the 'options' part.
I thought of something like
'GradObj','off', 'Hessian','off','DerivativeCheck','off');
options = optimoptions('fmincon','Display','off','Algorithm','sqp');
Is there a more correct set up for the 'options'?
When I use the fminunc:
'GradObj','off', 'Hessian','off','DerivativeCheck','off');
I get better results but sometimes the algorithm stops and throws me the following warning
Error using roots (line 27)
Input to ROOTS must not contain NaN or Inf.
Error in lineSearch
Error in lineSearch
Error in lineSearch
Error in lineSearch
Error in fminusub (line 189)
lineSearch(funfcn,x,dir,f,dirDerivative, ...
Error in fminunc (line 457)
[x,FVAL,GRAD,HESSIAN,EXITFLAG,OUTPUT] = fminusub(funfcn,x, ...
Error in unified_2 (line 92)


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Accepted Answer

Star Strider
Star Strider on 29 Dec 2017
If you run it with no stated options (using the defaults instead) what is the result?
The NaN or Inf problem results when you get either 0/0 or something/0. See if you can ‘trap’ a zero denominator in your code for ‘function’. If the denominator is zero, substitute 1E-8 for it. Make further small changes or change your options structure if that causes misleading results.
Since you have a ‘complicated’ function, you will likely have to have to experiment on your own with solutions.


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Star Strider
Star Strider on 29 Dec 2017
The second approach will work:
options=optimset( 'display','off');
[xx,fval,exitflag,output,lambda,grad,HH] = fmincon('function',x0,...
As I read the documentation, name-value pair arguments are not permitted in fmincon, so the first will likely throw an error.
Star Strider
Star Strider on 29 Dec 2017
As always, my pleasure!
Note that the correct call is:
options = optimset(@fmincon, 'display','off');
I am certain that you already discovered that.
If my Answer helped you solve your problem, please Accept it!

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