[Bug-gsl] Multidimensional Root-Finding (gnewton)

[Allan Leal]

Hello GSL,

I have detected that the solver *gnewton* does not call the *fdf* 
function. It only calls *f* and *df*.

This does not happen in the *newton* solver, which only uses the *fdf* 
function.

If you go to the function *gnewton_iterate* on file *gnewton.c*, you 
will only see the following calls:

int status = GSL_MULTIROOT_FN_EVAL_F (fdf, state->x_trial, f);
int status = GSL_MULTIROOT_FN_EVAL_DF (fdf, x, J);

However, if you go to the function *newton_iterate* on file *newton.c*, 
you will only see the following call instead:

int status = GSL_MULTIROOT_FN_EVAL_F_DF(fdf, x, f, J);

Note that in the above call, the function that defines both the function 
and jacobian are called, which may be used to improve performance.

Best regards,
Allan