Oriented diameter of graphs with diameter $4$ and given maximum edge girth (2507.23517v1)

Published 31 Jul 2025 in math.CO

Abstract: Let $G$ be a bridgeless graph. We introduce the maximum edge girth of $G$, denoted by $g^{*(G)=\max{l_G(e)\mid} e\in E(G)}$, where $l_G(e)$ is the edge girth of $e$, defined as the length of the shortest cycle containing $e$. Let $F(d,A)$ be the smallest value for which every bridgeless graph $G$ with diameter $d$ and $g^*(G)\in A$ admits a strong orientation $\overrightarrow{G}$ such that the diameter of $\overrightarrow{G}$ is at most $F(d,A)$. Let $f(d)=F(d,A)$, where $A={a\in \mathbb{N}\mid 2\leq a\leq 2d+1}$. Chv\'atal and Thomassen (JCT-B, 1978) obtained general bounds for $f(d)$ and showed that $f(2)=6$. Kwok et al. (JCT-B, 2010) proved that $9\leq f(3)\leq 11$. Wang and Chen (JCT-B, 2022) determined $f(3)=9$. In this paper, we give that $12\leq F(4,A^*)\leq 13$, where $A^{*={2,3,6,7,8,9}$.}