[Help-gsl] How do I set the fsolver type in gsl?

[Humbaba Gilgamesh]

Hi people,

how do I set the fsolver type in gsl? 
When I use fdfsolver the case is clear it goes like this:
constgsl_multifit_fdfsolver_type *T;gsl_multifit_fdfsolver *s;T 
=gsl_multifit_fdfsolver_lmsder;s 
=gsl_multifit_fdfsolver_alloc(T,n,p);gsl_multifit_fdfsolver_set(s,&f,&x.vector);
But how am I supposed to do it for a fsolver:
constgsl_multifit_fsolver_type *T;gsl_multifit_fsolver *s;T=?????
What I want to do is the following. I have a polynom which I want to 
fit to some 3D data. The fsolver should fit the coefficients of the 
polynom. I want to use fsolver because inside the fitting function I 
need to set all the coefficients to be positive.
Thanks for your help.