An O(n2) bound for the relaxation time of a Markov chain on cladograms

  • Authors:
  • Jason Schweinsberg

  • Affiliations:
  • University of California, Berkeley, California

  • Venue:
  • Random Structures & Algorithms
  • Year:
  • 2002

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Abstract

A cladogram is an unrooted tree with labeled leaves and unlabeled internal branchpoints of degree 3. Aldous has studied a Markov chain on the set of n-leaf cladograms in which each transition consists of removing a random leaf and its incident edge from the tree and then reattaching the leaf to a random edge of the remaining tree. Using coupling methods, Aldous showed that the relaxation time (i.e., the inverse of the spectral gap) for this chain is O(n3). Here, we use a method based on distinguished paths to prove an O(n2) bound for the relaxation time, establishing a conjecture of Aldous.