A matrix whose entries consist of the symbols +,-,0 is called a sign-pattern matrix. For a real matrix B, by sgnB we mean the sign pattern matrix in which each positive (respectively, negative, zero) entry is replaced by + (respectively, -, 0). For each $n imes n$ sign-pattern matrix A, there is a natural class of real matrics whose entries have the sign indicated by A. If $A = [a_{ij}]$ is an $n imes n$ sign-pattern matrix, then the sign-pattern class of A is defined by $$ (1.1) Q(A) = {B = [b_{ij}] $mid$ sgnb_{ij} = a_{ij} for all i and j in {1,2,...,n}}. $$</TEX>