Counting triangulations and other crossing-free structures approximately

Victor Alvarez, Karl Bringmann, Saurabh Ray, Raimund Seidel

    Research output: Contribution to journalArticle

    Abstract

    We consider the problem of counting straight-edge triangulations of a given set P of npoints in the plane. Until very recently it was not known whether the exact number of triangulations of P can be computed asymptotically faster than by enumerating all triangulations. We now know that the number of triangulations of P can be computed in O∗(2n) time [9], which is less than the lower bound of Ω(2.43n) on the number of triangulations of any point set [30]. In this paper we address the question of whether one can approximately count triangulations in sub-exponential time. We present an algorithm with sub-exponential running time and sub-exponential approximation ratio, that is, denoting by Λ the output of our algorithm and by cn the exact number of triangulations of P, for some positive constant c, we prove that cn ≤ Λ ≤ cn· 2°(n). This is the first algorithm that in sub-exponential time computes a (1 + o(1))-approximation of the base of the number of triangulations, more precisely, c ≤ Λn-1≤ (1 + o(1))c. Our algorithm can be adapted to approximately count other crossing-free structures on P, keeping the quality of approximation and running time intact. In this paper we show how to do this for matchings and spanning trees.

    Original languageEnglish (US)
    Pages (from-to)386-397
    Number of pages12
    JournalComputational Geometry: Theory and Applications
    Volume48
    Issue number5
    DOIs
    StatePublished - Jan 1 2015

    Fingerprint

    Triangulation
    Counting
    Exponential time
    Count
    Approximation
    Spanning tree
    Point Sets
    Straight
    Lower bound
    Output

    Keywords

    • Algorithmic geometry
    • Approximation algorithms
    • Counting algorithms
    • Crossing-free structures
    • Triangulations

    ASJC Scopus subject areas

    • Computer Science Applications
    • Geometry and Topology
    • Control and Optimization
    • Computational Theory and Mathematics
    • Computational Mathematics

    Cite this

    Counting triangulations and other crossing-free structures approximately. / Alvarez, Victor; Bringmann, Karl; Ray, Saurabh; Seidel, Raimund.

    In: Computational Geometry: Theory and Applications, Vol. 48, No. 5, 01.01.2015, p. 386-397.

    Research output: Contribution to journalArticle

    Alvarez, Victor ; Bringmann, Karl ; Ray, Saurabh ; Seidel, Raimund. / Counting triangulations and other crossing-free structures approximately. In: Computational Geometry: Theory and Applications. 2015 ; Vol. 48, No. 5. pp. 386-397.
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