Hamilton decompositions of regular expanders: Applications

  • Authors:
  • Daniela Kühn;Deryk Osthus

  • Affiliations:
  • -;-

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2014

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Abstract

In a recent paper, we showed that every sufficiently large regular digraph G on n vertices whose degree is linear in n and which is a robust outexpander has a decomposition into edge-disjoint Hamilton cycles. The main consequence of this theorem is that every regular tournament on n vertices can be decomposed into (n-1)/2 edge-disjoint Hamilton cycles, whenever n is sufficiently large. This verified a conjecture of Kelly from 1968. In this paper, we derive a number of further consequences of our result on robust outexpanders, the main ones are the following:(i)an undirected analogue of our result on robust outexpanders; (ii)best possible bounds on the size of an optimal packing of edge-disjoint Hamilton cycles in a graph of minimum degree @d for a large range of values for @d. (iii)a similar result for digraphs of given minimum semidegree; (iv)an approximate version of a conjecture of Nash-Williams on Hamilton decompositions of dense regular graphs; (v)a verification of the 'very dense' case of a conjecture of Frieze and Krivelevich on packing edge-disjoint Hamilton cycles in random graphs; (vi)a proof of a conjecture of Erdos on the size of an optimal packing of edge-disjoint Hamilton cycles in a random tournament.