Abstract

Graph Theory We introduce a variation of chip-firing games on connected graphs. These 'burn-off' games incorporate the loss of energy that may occur in the physical processes that classical chip-firing games have been used to model. For a graph G=(V,E), a configuration of 'chips' on its nodes is a mapping C:V→ℕ. We study the configurations that can arise in the course of iterating a burn-off game. After characterizing the 'relaxed legal' configurations for general graphs, we enumerate the 'legal' ones for complete graphs Kn. The number of relaxed legal configurations on Kn coincides with the number tn+1 of spanning trees of Kn+1. Since our algorithmic, bijective proof of this fact does not invoke Cayley's Formula for tn, our main results yield secondarily a new proof of this formula.

Highlights

  • Chip-firing games on graphs enjoy a rich literature

  • This article continues the published account of [20]—initiated in [15]—where we study a variant of chip-firing in which all games have finite length

  • We present a pair of algorithms that give a one-to-one correspondence between relaxed legal configurations on Kn+1. Let V (Kn+1) (1) Let V (Kn) and spanning trees of Kn+1

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Summary

Introduction

Chip-firing games on graphs enjoy a rich literature This is due to their surprising array of mathematical connections and to their utility in modeling certain kinds of physical systems. For the former, we find ties, e.g., to discrepancy theory [21], the Tutte polynomial [16], critical groups of graphs [5], G-parking functions [3], and stochastic processes [11]. This article continues the published account of [20]—initiated in [15]—where we study a variant of chip-firing in which all games have finite length These ‘burn-off’ games incorporate the loss of energy that may occur in the physical processes that classical chip-firing games have been used to model. For any basics we may have omitted, we point the reader to [8]

Description of the game
Reverse-firing and legal configurations
Characterizing relaxed legal configurations
Checking the legality of a configuration
The poset of legal configurations
Results for complete graphs
Enumerating legal configurations
Connections with spanning trees
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