On the connected components of a random permutation graph with a given number of edges

  • Authors:
  • Hüseyin Acan;Boris Pittel

  • Affiliations:
  • -;-

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

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Abstract

A permutation @s of [n] induces a graph G"@s on [n] - its edges are inversion pairs in @s. The graph G"@s is connected if and only if @s is indecomposable. Let @s(n,m) denote a permutation chosen uniformly at random among all permutations of [n] with m inversions. Let p(n,m) be the common value for the probabilities P(@s(n,m) is indecomposable) and P(G"@s"("n","m") is connected). We prove that p(n,m) is non-decreasing with m by constructing a Markov process {@s(n,m)} in which @s(n,m+1) is obtained by increasing one of the components of the inversion sequence of @s(n,m) by one. We show that, with probability approaching 1, G"@s"("n","m") becomes connected for m asymptotic to m"n=(6/@p^2)nlogn. We also find the asymptotic sizes of the largest and smallest components when the number of edges is moderately below the threshold m"n.