Constant Unary Constraints and Symmetric Real-Weighted Counting Constraint Satisfaction Problems

TL;DR

This paper investigates the role of constant unary constraints in the approximate counting complexity of symmetric real-weighted Boolean #CSPs, showing that at least one can be approximated and eliminated efficiently, enabling reductions.

Contribution

It demonstrates that in approximate counting, at least one constant unary constraint can be approximated and used to reduce #CSPs with symmetric constraints, extending previous exact counting results.

Findings

At least one constant unary constraint can be efficiently approximated in the approximate counting model.

The paper establishes polynomial-time AP-reductions from #CSPs with designated constraints to symmetric real-valued #CSPs.

Constant unary constraints are key to arity reduction and complexity classification in approximate counting.

Abstract

A unary constraint (on the Boolean domain) is a function from {0,1} to the set of real numbers. A free use of auxiliary unary constraints given besides input instances has proven to be useful in establishing a complete classification of the computational complexity of approximately solving weighted counting Boolean constraint satisfaction problems (or #CSPs). In particular, two special constant unary constraints are a key to an arity reduction of arbitrary constraints, sufficient for the desired classification. In an exact counting model, both constant unary constraints are always assumed to be available since they can be eliminated efficiently using an arbitrary nonempty set of constraints. In contrast, we demonstrate in an approximate counting model, that at least one of them is efficiently approximated and thus eliminated approximately by a nonempty constraint set. This fact directly leads to an efficient construction of polynomial-time randomized approximation-preserving Turing reductions (or AP-reductions) from #CSPs with designated constraints to any given #CSPs composed of symmetric real-valued constraints of arbitrary arities even in the presence of arbitrary extra unary constraints.