English

Connectivity of friends-and-strangers graphs on random pairs

Combinatorics 2022-12-07 v2

Abstract

Consider two graphs XX and YY, each with nn vertices. The friends-and-strangers graph FS(X,Y)\mathsf{FS}(X,Y) of XX and YY is a graph with vertex set consisting of all bijections σ:V(X)V(Y)\sigma :V(X) \mapsto V(Y), where two bijections σ\sigma, σ\sigma' are adjacent if and only if they differ precisely on two adjacent vertices of XX, and the corresponding mappings are adjacent in YY. The most fundamental question that one can ask about these friends-and-strangers graphs is whether or not they are connected. Alon, Defant, and Kravitz showed that if XX and YY are two independent random graphs in G(n,p)\mathcal{G}(n,p), then the threshold probability guaranteeing the connectedness of FS(X,Y)\mathsf{FS}(X,Y) is p0=n1/2+o(1)p_0=n^{-1/2+o(1)}, and suggested to investigate the general asymmetric situation, that is, XG(n,p1)X\in \mathcal{G}(n,p_1) and YG(n,p2)Y\in \mathcal{G}(n,p_2). In this paper, we show that if p1p2p02=n1+o(1)p_1 p_2 \ge p_0^2=n^{-1+o(1)} and p1,p2w(n)p0p_1, p_2 \ge w(n) p_0, where w(n)0w(n)\rightarrow 0 as nn\rightarrow \infty, then FS(X,Y)\mathsf{FS}(X,Y) is connected with high probability, which extends the result on p1=p2=pp_1=p_2=p, due to Alon, Defant, and Kravitz.

Keywords

Cite

@article{arxiv.2208.00801,
  title  = {Connectivity of friends-and-strangers graphs on random pairs},
  author = {Lanchao Wang and Yaojun Chen},
  journal= {arXiv preprint arXiv:2208.00801},
  year   = {2022}
}

Comments

16 pages, 1 fighres. This is a version revised mainly under very careful comments from the anonymous referees. arXiv admin note: substantial text overlap with arXiv:2009.07840 by other authors