i am currently working on creating mathematical models for my research and want a non linear equation solver library which i could integrate with my program .
i searched the web and found op++ which wasnt a free program .

I have previously used cminpack... Which is a port of the FORTRAN minpack. It works pretty good and should help yout out with your research.

Make sure you download the source from the "Distribution" section...

HTH's
sinnerFA