Degree two approximate Boolean #CSPs with variable weights

TL;DR

This paper classifies the computational complexity of approximately counting solutions in degree-two Boolean #CSPs with variable weights, showing a dichotomy between tractability and reductions to known hard problems.

Contribution

It extends the classification of Boolean #CSPs to degree-two instances with variable weights, establishing a clear dichotomy in complexity.

Findings

Dichotomy between tractable and hard cases

Reduction to #BIS or #PM in hard cases

Extension of previous classifications to degree-two with weights

Abstract

A counting constraint satisfaction problem (#CSP) asks for the number of ways to satisfy a given list of constraints, drawn from a fixed constraint language \Gamma. We study how hard it is to evaluate this number approximately. There is an interesting partial classification, due to Dyer, Goldberg, Jalsenius and Richerby, of Boolean constraint languages when the degree of instances is bounded by d>=3 - every variable appears in at most d constraints - under the assumption that "pinning" is allowed as part of the instance. We study the d=2 case under the stronger assumption that "variable weights" are allowed as part of the instance. We give a dichotomy: in each case, either the #CSP is tractable, or one of two important open problems, #BIS or #PM, reduces to the #CSP.