The Perfect Matching Reconfiguration Problem

TL;DR

This paper investigates the computational complexity of transforming one perfect matching into another via flip operations across various graph classes, establishing both hardness results and efficient algorithms for specific graph types.

Contribution

It proves PSPACE-completeness for split and bounded bandwidth bipartite graphs, and provides polynomial-time algorithms for strongly orderable, outerplanar, and cograph classes.

Findings

PSPACE-completeness for split and bounded bandwidth bipartite graphs

Polynomial-time solvability for strongly orderable, outerplanar, and cograph graphs

Existence of linear flip sequences with polynomial-time construction

Abstract

We study the perfect matching reconfiguration problem: Given two perfect matchings of a graph, is there a sequence of flip operations that transforms one into the other? Here, a flip operation exchanges the edges in an alternating cycle of length four. We are interested in the complexity of this decision problem from the viewpoint of graph classes. We first prove that the problem is PSPACE-complete even for split graphs and for bipartite graphs of bounded bandwidth with maximum degree five. We then investigate polynomial-time solvable cases. Specifically, we prove that the problem is solvable in polynomial time for strongly orderable graphs (that include interval graphs and strongly chordal graphs), for outerplanar graphs, and for cographs (also known as $P_4$-free graphs). Furthermore, for each yes-instance from these graph classes, we show that a linear number of flip operations is sufficient and we can exhibit a corresponding sequence of flip operations in polynomial time.