Free energy, entropy, and lattice gas representations

The entropy formulation for profile equations of pair-interacting classical fluids is recalled, and the special case of next-neighbor interacting fluids in one dimension carried out in auxiliary field form. Attention shifts to the general lattice gas with multi-state sites. The exact entropy is obtained for next-neighbor interacting Cayley trees, and generalized to simplicial trees with adjacent surface interactions. We then find the continuum limit of the tree models in their usual lattice gas version and put this in the general context of many-body interacting classical systems.