Higher Secondary Polytopes for Two-Dimensional Zonotopes

Abstract

Very recently, Galashin, Postnikov, and Williams introduced the notion of higher secondary polytopes, generalizing the secondary polytope of Gelfand, Kapranov, and Zelevinsky. Given an $n$-point configuration $\mathcal{A}$ in ${\mathbb{R}}^{d-1}$, they define a family of convex $(n-d)$-dimensional polytopes ${\hat{\Sigma }}_1,\dots ,{\hat{\Sigma }}_{n-d}$. The $1$-skeletons of this family of polytopes are the flip graphs of certain combinatorial configurations which generalize triangulations of $\text{conv}\mathcal{A}$. We restrict our attention to $d=2$. First, we relate the $1$-skeleton of the Minkowski sum ${\hat{\Sigma }}_k+{\hat{\Sigma }}_{k-1}$ to the flip graph of "hypertriangulations" of the deleted $k$-sum of $\mathcal{A}$ when $\mathcal{A}$ consists of distinct points. Second, we compute the diameter of ${\hat{\Sigma }}_k$ and ${\hat{\Sigma }}_k+{\hat{\Sigma }}_{k-1}$ for all $k$.

20 pages, 11 figures