On the number of 4-cycles in a tournament
Abstract
If is an -vertex tournament with a given number of -cycles, what can be said about the number of its -cycles? The most interesting range of this problem is where is assumed to have cyclic triples for some and we seek to minimize the number of -cycles. We conjecture that the (asymptotic) minimizing 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 -cycles. These questions can be equivalently stated in terms of transitive subtournaments. Namely, given the number of transitive triples in , how many transitive quadruples can it have? As far as we know, this is the first study of inducibility in tournaments.
Keywords
Cite
@article{arxiv.1405.1576,
title = {On the number of 4-cycles in a tournament},
author = {Nati Linial and Avraham Morgenstern},
journal= {arXiv preprint arXiv:1405.1576},
year = {2015}
}
Comments
11 pages, 5 figures