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On the structure of Dense graphs with bounded clique number

Part of: Graph theory

Published online by Cambridge University Press:  05 June 2020

Heiner Oberkampf  and
Mathias Schacht
Heiner Oberkampf
Affiliation:
Institut für Informatik, Universität Augsburg, Augsburg, Germany
Mathias Schacht*
Affiliation:
Fachbereich Mathematik, Universität Hamburg, Hamburg, Germany
*
*Corresponding author. Email: schacht@math.uni-hamburg.de
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Abstract

We study structural properties of graphs with bounded clique number and high minimum degree. In particular, we show that there exists a function L = L(r,ɛ) such that every Kr-free graph G on n vertices with minimum degree at least ((2r–5)/(2r–3)+ɛ)n is homomorphic to a Kr-free graph on at most L vertices. It is known that the required minimum degree condition is approximately best possible for this result.

For r = 3 this result was obtained by Łuczak (2006) and, more recently, Goddard and Lyle (2011) deduced the general case from Łuczak’s result. Łuczak’s proof was based on an application of Szemerédi’s regularity lemma and, as a consequence, it only gave rise to a tower-type bound on L(3, ɛ). The proof presented here replaces the application of the regularity lemma by a probabilistic argument, which yields a bound for L(r, ɛ) that is doubly exponential in poly(ɛ).

MSC classification

Primary: 05C35: Extremal problems
Secondary: 05C75: Structural characterization of families of graphs
Type
Paper
Information
Combinatorics, Probability and Computing , Volume 29 , Issue 5 , September 2020 , pp. 641 - 649
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Copyright
© Cambridge University Press 2020

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Footnotes

†

The second author was supported by the Heisenberg Programme of the Deutsche Forschungsgemeinschaft.

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