On the difference between the Szeged and Wiener index

Marthe Bonamy; Martin Knor; Borut Lužar; Alexandre Pinlou; Riste Škrekovski

doi:10.1016/j.amc.2017.05.047

paper

On the difference between the Szeged and Wiener index

arXiv:1602.05184 · doi:10.1016/j.amc.2017.05.047

Abstract

We prove a conjecture of Nadjafi-Arani, Khodashenas and Ashrafi on the difference between the Szeged and Wiener index of a graph. Namely, if $G$ is a 2-connected non-complete graph on $n$ vertices, then $S z (G) - W (G) \geq 2 n - 6$ . Furthermore, the equality is obtained if and only if $G$ is the complete graph $K_{n - 1}$ with an extra vertex attached to either $2$ or $n - 2$ vertices of $K_{n - 1}$ . We apply our method to strengthen some known results on the difference between the Szeged and Wiener index of bipartite graphs, graphs of girth at least five, and the difference between the revised Szeged and Wiener index. We also propose a stronger version of the aforementioned conjecture.