English

Simplicial complexes with many facets are vertex decomposable

Combinatorics 2024-12-06 v2 Commutative Algebra

Abstract

Suppose Δ\Delta is a pure simplicial complex on nn vertices having dimension dd and let c=nd1c = n-d-1 be its codimension in the simplex. Terai and Yoshida proved that if the number of facets of Δ\Delta is at least (nc)2c+1\binom{n}{c}-2c+1, then Δ\Delta is Cohen-Macaulay. We improve this result by showing that these hypotheses imply the stronger condition that Δ\Delta is vertex decomposable. We give examples to show that this bound is optimal, and that the conclusion cannot be strengthened to the class of matroids or shifted complexes. We explore an application to Simon's Conjecture and discuss connections to other results from the literature.

Keywords

Cite

@article{arxiv.2403.07316,
  title  = {Simplicial complexes with many facets are vertex decomposable},
  author = {Anton Dochtermann and Ritika Nair and Jay Schweig and Adam Van Tuyl and Russ Woodroofe},
  journal= {arXiv preprint arXiv:2403.07316},
  year   = {2024}
}

Comments

In this version, included a connection to geometric vertex decomposability in the end. Modified the statement of Lemma 3.3, and proof of Theorem 1, along with other minor changes. Set to appear in the Electronic Journal of Combinatorics

R2 v1 2026-06-28T15:16:43.349Z