Hamiltonian cycles above expectation in r-graphs and quasi-random r-graphs

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Abstract

Let Hr(n,p) denote the maximum number of Hamiltonian cycles in an n-vertex r-graph with density p∈(0,1). The expected number of Hamiltonian cycles in the random r-graph model Gr(n,p) is E(n,p)=pn(n−1)!/2 and in the random graph model Gr(n,m) with m=p(nr) it is, in fact, slightly smaller than E(n,p). For graphs, H2(n,p) is proved to be only larger than E(n,p) by a polynomial factor and it is an open problem whether a quasi-random graph with density p can be larger than E(n,p) by a polynomial factor. For hypergraphs (i.e. r≥3) the situation is drastically different. For all r≥3 it is proved that Hr(n,p) is larger than E(n,p) by an exponential factor and, moreover, there are quasi-random r-graphs with density p whose number of Hamiltonian cycles is larger than E(n,p) by an exponential factor.

Original languageEnglish
Pages (from-to)195-222
Number of pages28
JournalJournal of Combinatorial Theory. Series B
Volume153
DOIs
StatePublished - Mar 2022

Bibliographical note

Funding Information:
This research was supported by the Israel Science Foundation (grant No. 1082/16 ).

Publisher Copyright:
© 2021 Elsevier Inc.

Keywords

  • Hamiltonian cycle
  • Quasi-random hypergraph
  • r-graph

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Discrete Mathematics and Combinatorics
  • Computational Theory and Mathematics

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