Packing cliques in graphs with independence number 2

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Abstract

Let G be a graph with no three independent vertices. How many edges of G can be packed with edge-disjoint copies of Kk More specifically, let fk(n, m) be the largest integer t such that, for any graph with n vertices, m edges, and independence number 2, at least t edges can be packed with edge-disjoint copies of Kk. Turán's theorem together with Wilson's Theorem assert that fk(n, m) = (1 -o(1))n2/4 if m ≈ n2/4. A conjecture of Erdos states that f3(n, m) > (1 - o(1))n2/4 for all plausible m. For any e > 0, this conjecture was open even if m ≤ n2(1/4 + e). Generally, f k(n, m) may be significantly smaller than n2/4. Indeed, for k = 7 it is easy to show that f7(n, m) ≤ 21/90 n2 for m ≈ 0.3n2. Nevertheless, we prove the following result. For every k ≥ 3 there exists γ > 0 such that if m ≤ n2(1/4 + γ) then fk(n, m) ≥ (1 - o(1)))n2/4. In the special case k = 3 we obtain the reasonable bound γ ≥ 10-4. In particular, the above conjecture of Erdos holds whenever G has fewer than 0.250.1n2 edges.

Original languageEnglish
Pages (from-to)805-817
Number of pages13
JournalCombinatorics Probability and Computing
Volume16
Issue number5
DOIs
StatePublished - Sep 2007

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Statistics and Probability
  • Computational Theory and Mathematics
  • Applied Mathematics

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