English

Pairs of a tree and a nontree graph with the same status sequence

Combinatorics 2019-01-29 v1

Abstract

The status of a vertex xx in a graph is the sum of the distances between xx and all other vertices. Let GG be a connected graph. The status sequence of GG is the list of the statuses of all vertices arranged in nondecreasing order. GG is called status injective if all the statuses of its vertices are distinct. Let GG be a member of a family of graphs F\mathscr{F} and let the status sequence of GG be s.s. GG is said to be status unique in F\mathscr{F} if GG is the unique graph in F\mathscr{F} whose status sequence is s.s. In 2011, J.L. Shang and C. Lin posed the following two conjectures. Conjecture 1: A tree and a nontree graph cannot have the same status sequence. Conjecture 2: Any status injective tree is status unique in all connected graphs. We settle these two conjectures negatively. For every integer n10,n\ge 10, we construct a tree TnT_n and a unicyclic graph Un,U_n, both of order n,n, with the following two properties: (1) TnT_n and UnU_n have the same status sequence; (2) for n15,n\ge 15, if nn is congruent to 33 modulo 44 then TnT_n is status injective and among any four consecutive even orders, there is at least one order nn such that TnT_n is status injective.

Keywords

Cite

@article{arxiv.1901.09547,
  title  = {Pairs of a tree and a nontree graph with the same status sequence},
  author = {Pu Qiao and Xingzhi Zhan},
  journal= {arXiv preprint arXiv:1901.09547},
  year   = {2019}
}

Comments

14 pages, 11 figures