I'm currently trying to solve a system of (3) nonlinear equations of (3) variables which are the baryonic density, the isospin asymmetry and and the density of a fluid with the Broyden's method (a quasi-Newton method) included in the GSL.
The problem is that I don't know how to avoid negative roots. I don't want them because it's obviously nonphysical. I guess I should use some conditions but I don't know which ones... I'm programming in C.
Could you help please?
Thanks in advance!