Diagrammatical Techniques for Two-Dimensional Ising Models. I

Abstract

Techniques of division of a lattice site and integration of lattice sites are proposed in the diagrammatical method for the two-dimensional Ising model. It is shown that the calculations for systems on various lattices are reduced to those for a system on a square lattice, with the aid of the techniques. The technique of integration, in particular, is always useful for the Ising model on the dual lattice, when the consideration of the free fermion model is useful.