+1">Purpose</FONT></B>
<PRE>
  To compute unitary matrices Q1, Q2, and Q3 for a complex 2-by-2
  regular pencil aAB - bD, with A, B, D upper triangular, such that
  Q3' A Q2, Q2' B Q1, Q3' D Q1 are still upper triangular, but the
  eigenvalues are in reversed order. The matrices Q1, Q2, and Q3 are
  represented by

       (  CO1  SI1  )       (  CO2  SI2  )       (  CO3  SI3  )
  Q1 = (            ), Q2 = (            ), Q3 = (            ).
       ( -SI1' CO1  )       ( -SI2' CO2  )       ( -SI3' CO3  )

 