Article
Keywords:
sign pattern; inertia; inertia set; unique inertia
Summary:
The inertia set of a symmetric sign pattern $A$ is the set $i(A)=\lbrace i(B) \mid B=B^T \in Q(A)\rbrace $, where $i(B)$  denotes the inertia of real symmetric matrix  $B$, and $Q(A)$ denotes the sign pattern class of  $A$. In this paper, a complete characterization on the inertia set of the nonnegative symmetric sign pattern $A$ in which each diagonal entry is zero and all off-diagonal entries are positive is obtained. Further, we also consider the bound for the numbers of nonzero entries in the nonnegative symmetric sign patterns  $A$ with zero diagonal that require unique inertia.
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