 that small perturbations in A can make one or
                more of the eigenvalues have a non-negative real
                part;
                if DICO = 'D' this means that while the matrix A
                (or the factor S) has computed eigenvalues inside
                the unit circle, it is nevertheless only just
                convergent, in the sense that small perturbations
                in A can make one or more of the eigenvalues lie
                outside the unit circle;
             