Graph edge contraction and subdivisions for adjacency polytopes (1912.02841v2)

Abstract: Adjacency polytopes, a.k.a. symmetric edge polytopes, associated with undirected graphs have been defined and studied in several seemingly independent areas including number theory, discrete geometry, and dynamical systems. In particular, the authors are motivated by the tropical intersections problem derived from the Kuramoto equations. Regular subdivisions of adjacency polytopes are instrumental in solving these problems. This paper explores connections between the regular subdivisions of an adjacency polytope and the contraction of the underlying graph along an edge. We construct a special regular subdivision whose cells are in one-to-one correspondence with facets of an adjacency polytope associated with an edge-contraction of the original graph. Moreover, this subdivision induces a decomposition of the original graph into ``cell subgraphs''. We explore the combinatorial, graph-theoretic, and matroidal aspects of this connection.