the study is focused on some special sign pattern matrices.A class of spectrally and inertially arbitrary zero-nonzero pattern is given.It is proved that the Hessenberg-matrix is the minimal inertially arbitrary sign pattern.An almost inertially arbitrary sign pattern that is constructed by the direct sum from those of lower order is introduced.Based on the property of matrix-decomposition for analyzing S-shaped sign pattern matrix
a necessary condition on the spectrally arbitrary sign pattern matrix is characterized.
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references
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