I've been given the fundamental equation of a magnetic system .U(S,N,I)=... I have to calculate some thermodynamic potentials such as U[T] etc. One of them is the so called magnetic enthalpy and the expression for it is U[p,B]. Another one is U[p]. How do I calculate it? I don't even know what it means. Since I'm only used to pression, volume etc. I don't know what p is. If S is entropy, I the equivalent of volume and B (magnetic field or whatever) the equivalent of pressure. WHat is p?