LINEAR ALGEBRA AND ITS APPLICATIONS, vol.414, no.2-3, pp.547-559, 2006 (SCI-Expanded)
In this paper we give an alternative proof of the constant inertia theorem for convex compact sets of complex matrices. It is shown that the companion matrix whose non-trivial column is negative satisfies the directional Lyapunov condition (inclusion) for real multiplier vectors. An example of a real matrix polytope that satisfies the directional Lyapunov condition for real multiplier vectors and which has nonconstant inertia is given. A new stability criterion for convex compact sets of real Z-matrices is given. This criterion uses only real vectors and positive definite diagonal matrices. (c) 2005 Elsevier Inc. All rights reserved.