English

Maximum density of vertex-induced perfect cycles and paths in the hypercube

Combinatorics 2020-09-22 v1

Abstract

Let HH and KK be subsets of the vertex set V(Qd)V(Q_d) of the dd-cube QdQ_d (we call HH and KK configurations in QdQ_d). We say KK is an \emph{exact copy} of HH if there is an automorphism of QdQ_d which sends HH to KK. If dd is a positive integer and HH is a configuration in QdQ_d, we define π(H,d)\pi(H,d) to be the limit as nn goes to infinity of the maximum fraction, over all subsets SS of V(Qn)V(Q_n), of sub-dd-cubes of QnQ_n whose intersection with SS is an exact copy of HH. We determine π(C8,4)\pi(C_8,4) and π(P4,3)\pi(P_4,3) where C8C_8 is a "perfect" 8-cycle in Q4Q_4 and P4P_4 is a "perfect" path with 4 vertices in Q3Q_3, and make conjectures about π(C2d,d)\pi(C_{2d},d) and π(Pd+1,d)\pi(P_{d+1},d) for larger values of dd. In our proofs there are connections with counting the number of sequences with certain properties and with the inducibility of certain small graphs. In particular, we needed to determine the inducibility of two vertex disjoint edges in the family of bipartite graphs.

Keywords

Cite

@article{arxiv.2009.09037,
  title  = {Maximum density of vertex-induced perfect cycles and paths in the hypercube},
  author = {John Goldwasser and Ryan Hansen},
  journal= {arXiv preprint arXiv:2009.09037},
  year   = {2020}
}

Comments

11 pages, 0 figures