A Symmetry-Breaking Node Equivalence for Pruning the Search Space in Backtracking Algorithms

Abstract

We introduce a new equivalence on graphs, defined by its symmetry-breaking capability. We first present a framework for various backtracking search algorithms, in which the equivalence is used to prune the search tree. Subsequently, we define the equivalence and an optimization problem with the goal of finding an equivalence partition with the highest pruning potential. We also position the optimization problem into the computational-complexity hierarchy. In particular, we show that the verifier lies between P and NP -complete problems. Striving for a practical usability of the approach, we devise a heuristic method for general graphs and optimal algorithms for trees and cycles.

Keywords

• graph equivalence
• symmetry breaking
• backtracking
• monomorphism search
• search tree pruning
• graph algorithm