Distance k-sectors exist

  • Authors:
  • Keiko Imai;Akitoshi Kawamura;Jiři Matoušek;Daniel Reem;Takeshi Tokuyama

  • Affiliations:
  • Chuo University, Tokyo, Japan;University of Toronto, Toronto, ON, Canada;Charles University, Prague, Czech Rep;The Technion, Haifa, Israel;Tohoku University, Sendai, Japan

  • Venue:
  • Proceedings of the twenty-sixth annual symposium on Computational geometry
  • Year:
  • 2010

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Abstract

The bisector of two nonempty sets P and Q in a metric space is the set of all points with equal distance to P and to Q. A distance k-sector of P and Q, where k ≥ 2 is an integer, is a (k-1)-tuple (C1, C2, ..., Ck-1) such that Ci is the bisector of Ci-1 and Ci+1 for every i= 1, 2, ..., k-1, where C0 = P and Ck = Q. This notion, for the case where P and Q are points in Euclidean plane, was introduced by Asano, Matousek, and Tokuyama, motivated by a question of Murata in VLSI design. They established the existence and uniqueness of the distance trisector in this special case. We prove the existence of a distance k-sector for all k and for every two disjoint, nonempty, closed sets P and Q in Euclidean spaces of any (finite) dimension, or more generally, in proper geodesic spaces (uniqueness remains open). The core of the proof is a new notion of k-gradation for P and Q, whose existence (even in an arbitrary metric space) is proved using the Knaster-Tarski fixed point theorem, by a method introduced by Reem and Reich for a slightly different purpose.