摘要
A matrix A∈R<sup>nn</sup> is called an M-matrix if A = sI- B, where B≥0 and s≥ρ（B）, the spectral radius of B. By Γ（A） we denote the directed graph associated with a matrix A. The reflexive-transitive closure of F（A） is defined to be = △∪Γ（A）∪Γ<sup>2</sup>（A）∪…, where symbol △ denotes the diagonal graph.
