An Importance Sampling Scheme on Dual Factor Graphs - II. Models with Strong Couplings
We consider the problem of estimating the partition function of the two-dimensional ferromagnetic Ising and Potts models in an external magnetic field. The estimation is done via importance sampling in the dual of the Forney factor graph representing the models. We present importance sampling schemes that can efficiently compute an estimate of the partition function in a wide range of model parameters. Emphasis is on models in which a subset of the coupling parameters is strong.