[Scilab-users] Having a Problem with fsolve

[Samuel Gougeon]

Hello,

Le 15/10/2018 à 20:39, rsherry8 a écrit :
> I am trying to solve a system of two non-linear equations using 
> fsolve. I define the following two functions:
>
> function z=g1(x,y)
> z = x^2 + y^2
> endfunction
>
> function z=g2(x,y)
> z = x^4 + y^4 - 20
> endfunction
>
> When I type something like: g2(2,2)
> I get 12 which is right.
>
> I then run the following command:
>     [xres]=fsolve([0,0],g1,g2);

If it is provided, g2() must be the jacobian of g1(): it must compute 
and evaluate the partial derivatives of g1(), with respect to x and to y.
That's definitely not the case with your g2(). It should rather return 
something like [2*x 2*y].

For what you likely want to do, here are two examples (extracted from a 
document of mine in french, sorry):


Actually, the fsolve() page is rather poor : both given examples are 
about a single variable.
https://help.scilab.org/docs/6.0.1/en_US/fsolve.html

fsolve() is a key function. We should improve its help page.

HTH
Samuel

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