On planar intersection graphs with forbidden subgraphs

  • Authors:
  • János Pach;Micha Sharir

  • Affiliations:
  • Courant Institute of Mathematical Sciences, New York University, New York, New York 10012;Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 and School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel

  • Venue:
  • Journal of Graph Theory
  • Year:
  • 2008

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Abstract

Let ${\cal C}$ be a family of n compact connected sets in the plane, whose intersection graph $G({\cal C})$ has no complete bipartite subgraph with k vertices in each of its classes. Then $G({\cal C})$ has at most n times a polylogarithmic number of edges, where the exponent of the logarithmic factor depends on k. In the case where ${\cal C}$ consists of convex sets, we improve this bound to O(n log n). If in addition k = 2, the bound can be further improved to O(n). © 2008 Wiley Periodicals, Inc. J Graph Theory 59: 205–214, 2008