Limits of dense graph sequences

  • Authors:
  • László Lovász;Balázs Szegedy

  • Affiliations:
  • Microsoft Research, One Microsoft Way, Redmond, WA 98052, USA;Microsoft Research, One Microsoft Way, Redmond, WA 98052, USA

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2006

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Abstract

We show that if a sequence of dense graphs G"n has the property that for every fixed graph F, the density of copies of F in G"n tends to a limit, then there is a natural ''limit object,'' namely a symmetric measurable function W:[0,1]^2-[0,1]. This limit object determines all the limits of subgraph densities. Conversely, every such function arises as a limit object. We also characterize graph parameters that are obtained as limits of subgraph densities by the ''reflection positivity'' property. Along the way we introduce a rather general model of random graphs, which seems to be interesting on its own right.