Cutting dense point sets in half

  • Authors:
  • Herbert Edelsbrunner;Pavel Valtr;Emo Welzl

  • Affiliations:
  • Dept. Comput. Sci., Univ. Illinois at Urbana- Champaign, Urbana, Illinois;Graduiertenkolleg 'Algorithmische Diskrete Mathematik', Freie Univ. Berlin, 14195 Berlin, Germany and Dept. Applied Math., Malostranské nám. 25, Charles Univ., 118 00 Praha 1, Czech Repu ...;Inst. Informatik, Freie Univ. Berlin, 14195 Berlin, Germany

  • Venue:
  • SCG '94 Proceedings of the tenth annual symposium on Computational geometry
  • Year:
  • 1994

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Abstract

A halving hyperplane of a set S of n points in Rd contains d affinely independent points of S so that equally many of the points off the hyperplane lie in each of the two half-spaces. We prove bounds on the number of halving hyperplanes under the condition that the ratio of largest over smallest distance between any two points is at most &dgr;n1/d, &dgr; some constant. Such a set S is called dense.In d=2 dimensions, the number of halving lines for a dense set can be as much as &OHgr;(nlogn), and it cannot exceed O(n5/4/log*n). The upper bound improves over the current best bound of O(n3/2/log*n) which holds more generally without any density assumption. In d=3 dimensions we show that O(n7/3) is an upper bound on the number of halving planes for a dense set. The proof is based on a metric argument that can be extended to d≥4 dimensions, where it leads to O(nd−2/d) as an upper bound for the number of halving hyperplanes.