Address.
S.T. Impram, R. Johnson, 
Dipartimento di Sistemi e Informatica,
 Universita di Firenze, Italy
 
R. Pavani, Dipartimento di Matematica, Politecnico di Milano, Italy
E-mail. johnson@ing.unifi
Abstract.
 We give detailed discussion of a procedure for determining the
robust $D$-stability of a $4\times 4$ real matrix. The procedure
begins from the Hurwitz stability criterion. The procedure is
applied to two numerical examples.
AMSclassification. 15A04; 34D15; 65F15.
Keywords. Diagonal stability, Cauchy indices.