Degree Kirchhoff Index of Bicyclic Graphs

Abstract Let $G$ be a connected graph with vertex set $V\left( G \right)$ .The degree Kirchhoff index of $G$ is defined as ${{S}^{\prime }}\left( G \right)\,=\,\sum{_{\left\{ u,v \right\}\,\subseteq \,V\left( G \right)}d\left( u \right)d\left( v \right)R\left( u,\,v \right)}$ , where $d\left( u \right)$ is the degree of vertex $u$ , and $R\left( u,\,v \right)$ denotes the resistance distance between vertices $u$ and $v$ . In this paper, we characterize the graphs having maximum and minimum degree Kirchhoff index among all $n$ -vertex bicyclic graphs with exactly two cycles.