Maximum-utility popular matchings with bounded instability

TL;DR

This paper investigates maximizing utility in popular matchings with limited instability, providing complexity results and an optimal algorithm for specific preference structures.

Contribution

It introduces a multivariate approach to find maximum-utility popular matchings with bounded blocking edges, including an optimal algorithm for instances with a master list.

Findings

Finding popular matchings with at most one blocking edge is NP-complete in general graphs.

The paper establishes hardness results for restricted instances.

An optimal algorithm is designed for bipartite graphs with preferences admitting a master list.

Abstract

In a graph where vertices have preferences over their neighbors, a matching is called popular if it does not lose a head-to-head election against any other matching when the vertices vote between the matchings. Popular matchings can be seen as an intermediate category between stable matchings and maximum-size matchings. In this paper, we aim to maximize the utility of a matching that is popular but admits only a few blocking edges. For general graphs already finding a popular matching with at most one blocking edge is NP-complete. For bipartite instances, we study the problem of finding a maximum-utility popular matching with a bound on the number (or more generally, the cost) of blocking edges applying a multivariate approach. We show classical and parameterized hardness results for severely restricted instances. By contrast, we design an algorithm for instances where preferences on one side admit a master list, and show that this algorithm is optimal.