How to make sure that fsolve gives only positive values as the solution

Question

kalpana 2014-11-27

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回答： Ninad Mauskar 2019-6-18

I have L equations to solve. I am using the following code to solve :

    fh = matlabFunction([equn(1:L)],'vars',{[lam(1:L)]});
    options = optimset('Display','off','TolFun',eps);
    [solu_fsolve,value] = fsolve(fh, [1:L] ,options ) ;

But, i am getting -ve answer as a solution of fsolve. But, i am expecting + ve solutions only. Is there anyway to make sure that fsolve gives only +ve solutions?

Please answer. Thanks in advance.

With best regards, kalpana

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Answer 1

Torsten 2014-11-27

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Square your unknowns in the functions you supply to fsolve.

E.g. if you want to solve

x(1)-5=0,

solve instead

y(1)^2-5=0.

After you get the solution y(1) from fsolve (in this case sqrt(5)), you only have to square it to get x(1) (in this case 5) - the solution of your original untransformed problem.

Best wishes

Torsten.