What good libraries are there for solving a system of non-linear equations in C++?

Question

In a C++ application I\'m coding, I need to solve a system of non-linear equations (N equations, N unknowns).

The systems I\'m solving will be rather sm

Answer 1

There is always GSL, but all the comments made in the other answers apply to this as well:

http://www.gnu.org/software/gsl/manual/html_node/Multidimensional-Root_002dFinding.html#index-nonlinear-systems-of-equations_002c-solution-of-2426