er and
                  the error bound.

  FACT    CHARACTER*1
          Specifies whether or not the real Schur factorization of
          the matrix Ac = inv(I_n + G*X)*A (if TRANA = 'N'), or
          Ac = A*inv(I_n + X*G) (if TRANA = 'T' or 'C'), is supplied
          on entry, as follows:
          = 'F':  On entry, T and U (if LYAPUN = 'O') contain the
                  factors from the real Schur factorization of the
                  matrix Ac;
          = 'N':  The Schur factorization of Ac will 