The levmar is GPL'ed ANSI C implementation of the Levenberg-Marquardt (LM)
optimization algorithm. The LM algorithm provides a numerical solution to the
problem of minimizing a function over a parameter space of a function. The
levmar library provides implementation of both unconstrained and constrained LM
algorithms (box, linear equation, and linear inequality constraints).

WWW: https://github.com/bjodah/levmar