 Double-normal pairs in the plane and on the sphereJános Pach and Konrad J. Swanepoel LSE Research Online Documents on Economics from London School of Economics and Political Science, LSE Library Abstract: A double-normal pair of a finite set S of points from Euclidean space is a pair of points {p p,q q} from S such that S lies in the closed strip bounded by the hyperplanes through p p and q q that are perpendicular to p pq q . A double-normal pair p pq q is strict if S∖{p p,q q} lies in the open strip. We answer a question of Martini and Soltan (2006) by showing that a set of n≥3 points in the plane has at most 3⌊n/2⌋ double-normal pairs. This bound is sharp for each n≥3 . In a companion paper, we have asymptotically determined this maximum for points in R 3 . Here we show that if the set lies on some 2 -sphere, it has at most 17n/4−6 double-normal pairs. This bound is attained for infinitely many values of n . We also establish tight bounds for the maximum number of strict double-normal pairs in a set of n points in the plane and on the sphere. Keywords: 200021-137574; 200020-144531 (search for similar items in EconPapers) Published in Beiträge zur Algebra und Geometrie / Contributions to Algebra and Geometry, 2015, 56(2), pp. 423-438. ISSN: 0138-4821 Downloads: (external link) Related works: Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text Persistent link: https://EconPapers.repec.org/RePEc:ehl:lserod:57687 Access Statistics for this paper More papers in LSE Research Online Documents on Economics from London School of Economics and Political Science, LSE Library LSE Library Portugal Street London, WC2A 2HD, U.K.. Contact information at EDIRC. |
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