Directional Interchangeability for Enhancing CSP Solving

Abstract

This paper introduces directional interchangeability, a weak form of neighborhood interchangeability [6]. The basic idea is that although two values of a variable may not be neighborhood interchangeable if we consider the whole neighborhood of the variable, they could be neighborhood interchangeable if we restrict the neighborhood to a subset of neighboring variables induced by a variable ordering.

In spite of the fact that the proposed concept cannot be used to remove redundant values while preserving problem satisfiability, it provides a mean to partition value domains into subsets of directionally interchangeable values that can be attempted simultaneously by a tree search.

Several experiments carried out on various binary CSPs, clearly indicate that variations of the Forward-Checking algorithm and the Maintaining Arc-Consistency algorithm that exploit directional interchangeability often outperform the original algorithms.