on
  of A   and B  . This is called the "closest-neighbour" strategy.
      22      22

</PRE>
<A name="References"><B><FONT SIZE="+1">References</FONT></B></A>
<PRE>
  [1] Kagstrom, B. and Westin, L.
      Generalized Schur Methods with Condition Estimators for
      Solving the Generalized Sylvester Equation.
      IEEE Trans. Auto. Contr., 34, pp. 745-751, 1989.

  [2] Bavely, C. and Stewart, G.W.
      An Algorithm for Computing Reducing Subspaces by Block
      Diagonalization.
      SIAM J. Numer. Ana