 and the matrix A has a controllable
                eigenvalue on the imaginary axis, or DICO = 'D'
                and A has a controllable eigenvalue on the unit
                circle;
          = 4:  the solution of Lyapunov equation failed because
                the equation is singular;
          = 5:  if DICO = 'C' and D is a nonzero matrix;
          = 6:  if JOBN = 'H' and the system is unstable.

</PRE>
<A name="Method"><B><FONT SIZE="+1">Method</FONT></B></A>
<PRE>
  The subroutine is based on 