  We study theoretical and computational properties of the pressure function
for subshifts of finite type on the integer lattice $\Z^d$, multidimensional
SOFT, which are called Potts models in mathematical physics. We show that the
pressure is Lipschitz and convex. We use the properties of convex functions to
show rigorously that the phase transition of the first order correspond exactly
to the points where the pressure is not differentiable. We give computable
upper and lower bounds for the pressure, which can be arbitrary close the
values of the pressure given a sufficient computational power. We apply our
numerical methods to confirm Baxter's heuristic computations for two
dimensional monomer-dimer model, and to compute the pressure and the density
entropy as functions of two variables for the two dimensional monomer-dimer
model.
