一个n阶实矩阵B的惯量是一个非负三元整数组i(B)=(r,s,t),其中r、s、t分别表示矩阵B的实部为正、负、零的特征值个数(特征值的重数也计算在内)。设A是一个n阶符号模式矩阵,A的惯量i(A)是指由全体与A有相同符号模式的实矩阵的惯量构成的集合。若对于任意满足条件r+s+t=n的非负三元整数组(s,r,t),都有(s,r,t)∈i(A),则称A是惯量任意的。完全刻画了4、5、6阶惯量任意的可约符号模式矩阵。
The inertia of a real matrix B of order n is the triple of nonnegative integers i(B) = (r,s ,t) in which r,s,t are the numbers of its eigenvalues (counting multiplicities) with positive, negative and zero real parts respectively. The inertia of an n x n sign pattern matrix A is the set of {i (A)Ii (A) = i (B) ,sgnB =A}. An n xn sign pattern matrix A is an inertially arbitrary pattern if (r,s,t) i(A) for every nonnegative triple ( r, s, t) with r + s + t = n. This article characterizes the reducible inertially arbitrary sign patterns of orders 4, 5 and 6.