  = 3:  the reordering of the real Schur form of the
                Hamiltonian matrix failed;
          = 4:  the Hamiltonian matrix has less than N stable
                eigenvalues;
          = 5:  the coefficient matrix U11 in the linear system
                X*U11 = U21 to determine X is singular to working
                precision;
          = 6:  BETA = 0 and D has not a maximal row rank;
          = 7:  the computation of Hankel singular values failed;
          = 8:  the separation of the ALPHA