Counting plane graphs: Perfect matchings, spanning cycles, and Kasteleyn's technique

  • Authors:
  • Micha Sharir;Adam Sheffer;Emo Welzl

  • Affiliations:
  • School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel and Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA;School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel;Institute for Theoretical Computer Science, ETH Zürich, CH-8092 Zürich, Switzerland

  • Venue:
  • Journal of Combinatorial Theory Series A
  • Year:
  • 2013

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Abstract

We derive improved upper bounds on the number of crossing-free straight-edge spanning cycles (also known as Hamiltonian tours and simple polygonizations) that can be embedded over any specific set of N points in the plane. More specifically, we bound the ratio between the number of spanning cycles (or perfect matchings) that can be embedded over a point set and the number of triangulations that can be embedded over it. The respective bounds are O(1.8181^N) for cycles and O(1.1067^N) for matchings. These imply a new upper bound of O(54.543^N) on the number of crossing-free straight-edge spanning cycles that can be embedded over any specific set of N points in the plane (improving upon the previous best upper bound O(68.664^N)). Our analysis is based on a weighted variant of Kasteleyn@?s linear algebra technique.