Abstract:
Investigation (started in [1]) of the first Legendre transformation for the logarithm
of the statistical sum in the Ising model is continued. The diagram expansion
of the Legendre transformation $\Phi$ is the analogue of the virial expansion in the nonideal
gas theory, however in contrast to the gas theory, in the case of the Ising model
the functional $\Phi$ contains nonstar graphs as well. Complete characterisation of these
graphs is given. The practical method of constructing the nonstar graphs (the compensation
method) is suggested.