Transforming spanning trees: A lower bound

  • Authors:
  • Kevin Buchin;Andreas Razen;Takeaki Uno;Uli Wagner

  • Affiliations:
  • Institute of Computer Science, Freie Universität Berlin, Germany;Institute of Theoretical Computer Science, ETH Zurich, Switzerland;National Institute of Informatics, Tokyo, Japan;Institute of Theoretical Computer Science, ETH Zurich, Switzerland

  • Venue:
  • Computational Geometry: Theory and Applications
  • Year:
  • 2009

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Abstract

For a planar point set we consider the graph whose vertices are the crossing-free straight-line spanning trees of the point set, and two such spanning trees are adjacent if their union is crossing-free. An upper bound on the diameter of this graph implies an upper bound on the diameter of the flip graph of pseudo-triangulations of the underlying point set. We prove a lower bound of @W(logn/loglogn) for the diameter of the transformation graph of spanning trees on a set of n points in the plane. This nearly matches the known upper bound of O(logn). If we measure the diameter in terms of the number of convex layers k of the point set, our lower bound construction is tight, i.e., the diameter is in @W(logk) which matches the known upper bound of O(logk). So far only constant lower bounds were known.