Purpose</FONT></B>
<PRE>
  To find the eigenvalues of the generalized matrix product

               S(1)           S(2)                 S(K)
       A(:,:,1)     * A(:,:,2)     * ... * A(:,:,K)

  where A(:,:,H) is upper Hessenberg and A(:,:,i), i &lt;&gt; H, is upper
  triangular, using a double-shift version of the periodic
  QZ method. In addition, A may be reduced to periodic Schur form:
  A(:,:,H) is upper quasi-triangular and all the other factors
  A(:,:,I) are upper triangular. Optionally, the 2-by-