fsolve for 2 equation with 2 variables
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Miroslav Mitev
le 13 Déc 2017
Commenté : Star Strider
le 13 Déc 2017
Here is my function, in order to shorten the expression here I add A and B, but in my original function they are inside F(1) and F(2) (i.e. that is not the problem), this is the error I get: Objective function is returning undefined values at initial point.
function F = myfun(x)
N=32;
K=5;
s=1;
b=0.1;
P=5;
A=-2*s^4*x(1)*N+2*s^4*x(1)*K+3*s^2*x(2)*log(2);
B=sqrt(8)*x(2)*s^2*log(2);
g=exprnd(1,1,N-K);
F(1) = sum((g.*(1-b*x(1))/(x(2)*log(2)))-1./g)+(N-K)*((A+sqrt(A^2-B^2))/((4*s^2/sqrt(8))*B))-N*P;
F(2) = b*(sum(log2((g*(1-b*x(1)/x(2)*log(2))))))-(N-K)*log2(1+(2*A^2+2*A*sqrt(A^2-B^2)-B^2)/((4/sqrt(8))*B*(A+(4/sqrt(8))*B+sqrt(A^2-B^2))));
end
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Star Strider
le 13 Déc 2017
What is the initial point you chose? Your function returns finite values for random non-zero arguments. It returns [NaN NaN] for [0 0] as an input.
The solution is most likely to use an initial point other than [0 0]. I would use rand(2,1).
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Matt J
le 13 Déc 2017
Since it is only a function of 2 variables, you could do a coarse surf() plot of norm(F) and find visually where the roots approximately lie. This would give you a better initial guess than simply randomizing.
Star Strider
le 13 Déc 2017
My pleasure.
It might be useful for you to post the symbolic expression you are coding as well as your code for it as a new Question, since that seems to be the problem.
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