I am looking for a library that provides solving a system of nonlinear
equations, but would love to have a proper generic C++ library.
Support for functors, etc. would be ideal.

GSL provides a set of C interfaces, but it is tough to go back to
passing arrays of function pointers and I have neither the time nor
capability to wrap it myself. (not to mention the pesky license)

For optimization libraries, I have found COIN-OR, which seems to be
the place where many of the researchers work. Is there an equivalent
standard place for algorithms like this using proper C++ design?

(and if anyone knows of any nice, functor-based multidimensional
interpolation libraries, that would be great as well).

Thanks for your help,
Jesse

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