New Characterizations of Core Imputations of Matching and $b$-Matching Games

TL;DR

This paper provides new characterizations of core imputations in various matching and $b$-matching games, revealing which correspond to LP dual solutions and exploring agent profit structures.

Contribution

It extends the understanding of core imputations beyond classic frameworks, especially for bipartite $b$-matching games, and clarifies their LP duality relationships.

Findings

Core imputations in assignment games are LP dual solutions.

Some core imputations in $b$-matching games do not correspond to LP dual solutions.

New characterizations of agent and team profits in core imputations.

Abstract

We give new characterizations of core imputations for the following games: * The assignment game. * Concurrent games, i.e., general graph matching games having non-empty core. * The unconstrained bipartite $b$-matching game (edges can be matched multiple times). * The constrained bipartite $b$-matching game (edges can be matched at most once). The classic paper of Shapley and Shubik \cite{Shapley1971assignment} showed that core imputations of the assignment game are precisely optimal solutions to the dual of the LP-relaxation of the game. Building on this, Deng et al. \cite{Deng1999algorithms} gave a general framework which yields analogous characterizations for several fundamental combinatorial games. Interestingly enough, their framework does not apply to the last two games stated above. In turn, we show that some of the core imputations of these games correspond to optimal dual solutions and others do not. This leads to the tantalizing question of understanding the origins of the latter. We also present new characterizations of the profits accrued by agents and teams in core imputations of the first two games. Our characterization for the first game is stronger than that for the second; the underlying reason is that the characterization of vertices of the Birkhoff polytope is stronger than that of the Balinski polytope.