English

Magic Positivity for the Ehrhart Polynomials of Partial Permutohedra

Combinatorics 2026-07-04 v1

Abstract

For positive integers m,nm,n, the partial permutohedron P(m,n)\mathcal{P}(m,n) is a lattice polytope constructed as the convex hull of vectors in {0,1,,n}m\{0, 1, \dots, n\}^m that have distinct non-zero entries. We prove that for nm1n \ge m-1, the Ehrhart polynomial of P(m,n)\mathcal{P}(m,n) is magic positive except for the single case (m,n)=(2,1)(m,n)=(2,1). In particular, the Ehrhart polynomial of the parking function polytope (integrally equivalent to P(m,m1)\mathcal{P}(m,m-1)) is magic positive for m3m \ge 3. For n<m1n<m-1, we discuss the magic positivity of the Ehrhart polynomial of P(m,n)\mathcal{P}(m,n) for n=1,2,3n=1,2,3. There exist infinitely many counterexamples with n<m1n<m-1 showing that the Ehrhart polynomial of P(m,n)\mathcal{P}(m,n) is not magic positive. This partially resolves an open problem proposed by Ferroni and Higashitani.

Keywords

Cite

@article{arxiv.2607.03854,
  title  = {Magic Positivity for the Ehrhart Polynomials of Partial Permutohedra},
  author = {Feihu Liu and Zihao Zhang},
  journal= {arXiv preprint arXiv:2607.03854},
  year   = {2026}
}

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20 pages