English

Algebraic connectivity of the second power of a graph

Combinatorics 2024-07-03 v4

Abstract

Denote the Laplacian of a graph GG by L(G)L(G) and its second smallest Laplacian eigenvalue by λ2(G)\lambda_2(G). If GG is a graph on n2n\ge 2 vertices, then it is shown that the second smallest eigenvalue of L(G)+1nL(G2)L(G) + \frac{1}{n} L(\overline{G^2}) is at least 1, where G2\overline{G^2} is the complement of the second power of G G . As a corollary of this result, it is shown that \begin{itemize} \item nλ2(G)λ2(G2), n \, \lambda_2(G) \ge \lambda_2(G^2), \item λ2(G)1DGn, \lambda_2(G) \ge 1-\frac{|D_G|}{n}, \item λ2(G)+λ2(\Gb)1, \lambda_2(G) + \lambda_2(\Gb) \ge 1, \end{itemize} where DG|D_G| is the number of vertices of eccentricity at least 3 in GG.

Keywords

Cite

@article{arxiv.2109.04568,
  title  = {Algebraic connectivity of the second power of a graph},
  author = {B. Afshari},
  journal= {arXiv preprint arXiv:2109.04568},
  year   = {2024}
}

Comments

8 pages, correct some typos, rewrite abstract, same as the version published in the JGT