Variational help

[flexten]

I have been scouring the net and librarys for a reference on a general field variational principal. The closest i can find is magnetic material principal and piezoelectric principle. Tiersten, some stuff in the crystal redbook, Holland, and some old BSTJ articles are all i can find for piezoelectric media. Can someone point me in the direction of the most general linear variational formulation ? T,S,E,D,H,B,entropy and temp. in triclinic material ?

Best