On the Number of 4-Cycles in a Tournament

Nati Linial, Avraham Morgenstern

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

If T is an n-vertex tournament with a given number of 3-cycles, what can be said about the number of its 4-cycles? The most interesting range of this problem is where T is assumed to have (Formula presented.) cyclic triples for some (Formula presented.) and we seek to minimize the number of 4-cycles. We conjecture that the (asymptotic) minimizing T is a random blow-up of a constant-sized transitive tournament. Using the method of flag algebras, we derive a lower bound that almost matches the conjectured value. We are able to answer the easier problem of maximizing the number of 4-cycles. These questions can be equivalently stated in terms of transitive subtournaments. Namely, given the number of transitive triples in T, how many transitive quadruples can it have? As far as we know, this is the first study of inducibility in tournaments.

Original languageAmerican English
Pages (from-to)266-276
Number of pages11
JournalJournal of Graph Theory
Volume83
Issue number3
DOIs
StatePublished - 1 Nov 2016

Bibliographical note

Publisher Copyright:
© 2015 Wiley Periodicals, Inc.

Keywords

  • extremal combinatorics
  • local graph theory
  • small cycles in tournaments
  • tournaments

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