The average eccentricity of a graph with prescribed girth

Abstract

Let $G$ be a connected graph of order $n$. The eccentricity $e(v)$ of a vertex $v$ is the distance from $v$ to a vertex farthest from $v$. The average eccentricity of $G$ is the mean of all eccentricities in $G$. We give upper bounds on the average eccentricity of $G$ in terms of order $n$, minimum degree $\delta$, and girth $g$. In addition, we construct graphs to show that, if for given $g$ and $\delta$, there exists a Moore graph of minimum degree $\delta$ and girth $g$, then the bounds are asymptotically sharp. Moreover, we show that the bounds can be improved for a graph of large degree $\Delta$.