The eccentric digraph ED(G) of G is the digraph that has the same vertex set as Gand the arc set defined by : there is an arc from u to v if and only if v is an eccentricvertex of u .

• 定义G的离心图(eccentric digraph)如下:顶点集为V (G) ,弧集满足:有一条弧从v到u当且仅当顶点u是v的一个离心点,记为ED(G)。