On sets defining few ordinary hyperplanes

Lin, Aaron and Swanepoel, Konrad (2020) On sets defining few ordinary hyperplanes. Discrete Analysis. ISSN 2397-3129

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Abstract

Let P be a set of n points in real projective d-space, not all contained in a hyperplane, such that any d points span a hyperplane. An ordinary hyperplane of P is a hyperplane containing exactly d points of P. We show that if d > 4, the number of ordinary hyperplanes of P is at least (nd−−11) − Od(n⌊(d−1)/2⌋) if n is sufficiently large depending on d. This bound is tight, and given d, we can calculate the exact minimum number for sufficiently large n. This is a consequence of a structure theorem for sets with few ordinary hyperplanes: For any d > 4 and K > 0, if n > CdK8 for some constant Cd > 0 depending on d and P spans at most K(nd−−11) ordinary hyperplanes, then all but at most Od(K) points of P lie on a hyperplane, an elliptic normal curve, or a rational acnodal curve. We also find the maximum number of (d+1)-point hyperplanes, solving a d-dimensional analogue of the orchard problem. Our proofs rely on Green and Tao’s results on ordinary lines, our earlier work on the 3-dimensional case, as well as results from classical algebraic geometry. MSC Codes 52C10, 52C35

Item Type:	Article
Official URL:	https://discreteanalysisjournal.com/about
Additional Information:	© 2020 The Authors
Divisions:	Mathematics
Subjects:	Q Science > QA Mathematics
Date Deposited:	10 Feb 2020 10:18
Last Modified:	08 May 2024 20:19
URI:	http://eprints.lse.ac.uk/id/eprint/103320

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