English

On a Simplex Inscribed in a Ball

Metric Geometry 2026-05-22 v2

Abstract

Let BnB_n be the nn-dimensional unit ball given by the inequality x1\|x\|\leq 1, where x\|x\| is the standard Euclid norm in Rn{\mathbb R}^n. For an nn-dimensional nondegenerate simplex SS, we denote by EE the ellipsoid of minimum volume which contains SS. Suppose SBnS\subset B_n, 0mn10\leq m\leq n-1. Let GG be any mm-dimensional face of SS and let HH be the opposite (nm1)(n-m-1)-dimensional face. Denote by gg and hh the centers of gravity of GG and HH respectively. Define yy as the intersection point of the line passing from gg to hh with the boundary of EE. Let us call the face GG suitable if yBn.y\in B_n. Earlier it was proved that each simplex SBnS\subset B_n has a suitable face of any dimension n1\leq n-1. We show the following. Let SS be inscribed in BnB_n. If some vertex of SS is suitable, then there exists a suitable face of any dimension n1\leq n-1 which contains this vertex.

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Cite

@article{arxiv.2505.15739,
  title  = {On a Simplex Inscribed in a Ball},
  author = {Mikhail Nevskii},
  journal= {arXiv preprint arXiv:2505.15739},
  year   = {2026}
}

Comments

8 pages

R2 v1 2026-07-01T02:29:09.062Z