the QZ algorithm failed;
          = 3:  if reordering of the generalized eigenvalues failed;
          = 4:  if after reordering, roundoff changed values of
                some complex eigenvalues so that leading eigenvalues
                in the generalized Schur form no longer satisfy the
                stability condition; this could also be caused due
                to scaling;
          = 5:  if the computed dimension of the solution does not
                equal N;
          = 6:  if the spectru