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

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

Answer 1

[Torsten]

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.

Answer 2

[Ninad Mauskar]

Hi Kalpana,

Add a couple of conditional clauses before the return line.

For example, I am looking to solve for x such that array1[0,0] which is determined using x = certain fixed value.

I added a conditional statement before the return line which states:

if x < 0:

array1[0,0] = 0

else:

array1[0,0] is calculated using a specified formula which takes x as an input.

I have a return line after the above lines:

return array1[0,0] - certain value

When i use fsolve now, fsolve only gives be positive values of x.

Hope this helps!

Cheers,

Ninad