Roots of Ehrhart polynomials arising from graphs

Abstract

Several polytopes arise from finite graphs. For edge and symmetric edge polytopes, in particular, exhaustive computation of the Ehrhart polynomials not merely supports the conjecture of Beck et al. that all roots a of Ehrhart polynomials of polytopes of dimension D satisfy -D ≤ Re(α) ≤ D -1, but also reveals some interesting phenomena for each type of polytope. Here we present two new conjectures: (1) the roots of the Ehrhart polynomial of an edge polytope for a complete multipartite graph of order d lie in the circle |z + d/4| ≤ d/4 or are negative integers, and (2) a Gorenstein Fano polytope of dimension D has the roots of its Ehrhart polynomial in the narrower strip -D2 ≤ Re(α) = D/2 - 1. Some rigorous results to sup-port them are obtained as well as for the original conjecture. The root distribution of Ehrhart polynomials of each type of polytope is plotted in figures. © 2011 Springer Science+Business Media, LLC.