English

On the number of 5-cycles in a tournament

Combinatorics 2017-01-17 v3

Abstract

We find an exact formula for the number of directed 5-cycles in a tournament in terms of its edge score sequence. We use this formula to find both upper and lower bounds on the number of 5-cycles in any nn-tournament. In particular, we show that the maximum number of 5-cycles is asymptotically equal to 34(n5)\frac{3}{4}{n \choose 5}, the expected number 5-cycles in a random tournament (p=12p=\frac{1}{2}), with equality (up to order of magnitude) for almost all tournaments. Note that this means that almost all nn-tournaments contain the maximum number of 55-cycles.

Keywords

Cite

@article{arxiv.1410.6828,
  title  = {On the number of 5-cycles in a tournament},
  author = {Natasha Komarov and John Mackey},
  journal= {arXiv preprint arXiv:1410.6828},
  year   = {2017}
}

Comments

22 pages, 3 figures