Loop series expansion with propagation diagrams

Abstract

The Bethe approximation is a successful method for approximating partition functions of probabilistic models associated with a graph. Recently, Chertkov and Chernyak derived an interesting formula called ‘loop series expansion’, which is an expansion of the partition function. The main term of the series is the Bethe approximation while other terms are labelled by subgraphs called generalized loops. In this paper, we derive a loop series expansion of binary pairwise Markov random fields with ‘propagation diagrams’, which describes rules as to how ‘first messages’ and ‘secondary messages’ propagate. Our approach allows us to express the loop series in the form of a polynomial with coefficients positive integers. Using the propagation diagrams, we establish a new formula that shows a relation between the exact marginal probabilities and their Bethe approximations.