   ALPHAR(i), ALPHAI(i), BETA(i) and SCAL(i), for
                      i = INFO+1,...,N should be correct.

</PRE>
<A name="Method"><B><FONT SIZE="+1">Method</FONT></B></A>
<PRE>
  A modified version of the periodic QZ algorithm is used [1], [2].

</PRE>
<A name="References"><B><FONT SIZE="+1">References</FONT></B></A>
<PRE>
  [1] Bojanczyk, A., Golub, G. H. and Van Dooren, P.
      The periodic Schur decomposition: algorithms and applications.
      In F.T. Luk (editor), Advanced Signal Processing Algorit