A modification of the original lmfit library to simplify its use and allow some parallelization.
Just add lmfit.c and lmfit.h to your projects (don't forget the license). Or add this as a submodule or with FetchContent and link to lmfit2. Curve fitting is also included.
This version allows parallelization with OpenMP. If your evaluate() function is very expensive,
this may accelerate computation by calling it in parallel when computing the Jacobian. If the function is simple
there will be no gain, or even a performance penalty due to threading overhead.
To enable multithreading enable LMFIT_OPENMP in CMake configuration. Or if you don't use Cmake, enable OpenMP
in your compiler and define the macro LMFIT_OPENMP when compiling lmfit.c.
main.cpp is just a dumb usage example derived from the original project.