Dungeons and Dragons: Combinatorics for the $dP_3$ Quiver

Abstract

In this paper, we utilize the machinery of cluster algebras, quiver mutations, and brane tilings to study a variety of historical enumerative combinatorics questions all under one roof. Previous work [Zha, LMNT14], which arose during the second author's monitorship of undergraduates, and more recently of both authors [LM17], analyzed the cluster algebra associated to the cone over $\mathbf{dP_3}$, the del Pezzo surface of degree $6$ ($\mathbb{CP}^2$ blown up at three points). By investigating sequences of toric mutations, those occurring only at vertices with two incoming and two outgoing arrows, in this cluster algebra, we obtained a family of cluster variables that could be parameterized by $\mathbb{Z}^3$ and whose Laurent expansions had elegant combinatorial interpretations in terms of dimer partition functions (in most cases). While the earlier work [Zha, LMNT14, LM17] focused exclusively on one possible initial seed for this cluster algebra, there are in total four relevant initial seeds (up to graph isomorphism). In the current work, we explore the combinatorics of the Laurent expansions from these other initial seeds and how this allows us to relate enumerations of perfect matchings on Dungeons to Dragons.