English

Barycentric cuts through a convex body

Combinatorics 2020-03-31 v1 Computational Geometry Probability

Abstract

Let KK be a convex body in Rn\mathbb{R}^n (i.e., a compact convex set with nonempty interior). Given a point pp in the interior of KK, a hyperplane hh passing through pp is called barycentric if pp is the barycenter of KhK \cap h. In 1961, Gr\"{u}nbaum raised the question whether, for every KK, there exists an interior point pp through which there are at least n+1n+1 distinct barycentric hyperplanes. Two years later, this was seemingly resolved affirmatively by showing that this is the case if p=p0p=p_0 is the point of maximal depth in KK. However, while working on a related question, we noticed that one of the auxiliary claims in the proof is incorrect. Here, we provide a counterexample; this re-opens Gr\"unbaum's question. It follows from known results that for n2n \geq 2, there are always at least three distinct barycentric cuts through the point p0Kp_0 \in K of maximal depth. Using tools related to Morse theory we are able to improve this bound: four distinct barycentric cuts through p0p_0 are guaranteed if n3n \geq 3.

Keywords

Cite

@article{arxiv.2003.13536,
  title  = {Barycentric cuts through a convex body},
  author = {Zuzana Patáková and Martin Tancer and Uli Wagner},
  journal= {arXiv preprint arXiv:2003.13536},
  year   = {2020}
}

Comments

19 pages, 7 figures

R2 v1 2026-06-23T14:32:08.319Z