I'm working on a minimization problem on three different "types" of variables of different physical nature. To be more specific, I have stiffness tensor subjected to positive, definiteness constraints derived from the elastic strain energy. This contains both linear and non-linear parts. Secondly, I have density which can be constrained (or bounded??) by a value between [0.8,1.6] g/cc. And thirdly i have another isotropic elastic moduli that I can specify a reasonable range for. I'm not sure how to set up the constrained function or in fact the whole minimization problem given the multiple variable spaced involved in this. Any help or references would greatly be appreciated.