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NAME
     zlags2 - compute 2-by-2 unitary matrices U, V  and  Q,  such
     that  if  ( UPPER ) then   U'*A*Q = U'*( A1 A2 )*Q = ( x 0 )
     ( 0 A3 ) ( x x ) and  V'*B*Q = V'*( B1 B2 )*Q = ( x 0 )  ( 0
     B3 ) ( x x )  or if ( .NOT.UPPER ) then   U'*A*Q = U'*( A1 0
     )*Q = ( x x )  ( A2 A3 ) ( 0 x ) and  V'*B*Q = V'*( B1 0 )*Q
     =  ( x x )  ( B2 B3 ) ( 0 x ) where   U = ( CSU SNU ), V = (
     CSV SNV ),

SYNOPSIS
     SUBROUTINE ZLAGS2( UPPER, A1, A2, A3, B1, B2, B3, CSU,  SNU,
               CSV, SNV, CSQ, SNQ )

     LOGICAL UPPER

     DOUBLE PRECISION A1, A3, B1, B3, CSQ, CSU, CSV

     COMPLEX*16 A2, B2, SNQ, SNU, SNV



     #include <sunperf.h>

     void zlags2(int upper, double a1, doublecomplex *a2,  double
               a3,  double b1, doublecomplex *b2, double b3, dou-
               ble *csu, doublecomplex *snu, double  *csv,  doub-
               lecomplex *snv, double *csq, doublecomplex *snq);

PURPOSE
     ZLAGS2 computes 2-by-2 unitary matrices U,  V  and  Q,  such
     that if ( UPPER ) then

           ( -CONJG(SNU)  CSU )      ( -CONJG(SNV) CSV )

       Q = (     CSQ      SNQ )
           ( -CONJG(SNQ)  CSQ )

     Z' denotes the conjugate transpose of Z.

     The rows of the transformed A and B are parallel.  Moreover,
     if  the  input  2-by-2  matrix  A  is  not  zero,  then  the
     transformed (1,1) entry of A  is  not  zero.  If  the  input
     matrices  A  and  B  are both not zero, then the transformed
     (2,2) element of B is not zero, except when the  first  rows
     of input A and B are parallel and the second rows are zero.


ARGUMENTS
     UPPER     (input) LOGICAL
               = .TRUE.: the input matrices A  and  B  are  upper
               triangular.
               = .FALSE.: the input matrices A and  B  are  lower
               triangular.

     A1        (input) DOUBLE PRECISION
               A2      (input) COMPLEX*16 A3      (input)  DOUBLE
               PRECISION  On entry, A1, A2 and A3 are elements of
               the input 2-by-2 upper (lower)  triangular  matrix
               A.

     B1        (input) DOUBLE PRECISION
               B2      (input) COMPLEX*16 B3      (input)  DOUBLE
               PRECISION  On entry, B1, B2 and B3 are elements of
               the input 2-by-2 upper (lower)  triangular  matrix
               B.

     CSU       (output) DOUBLE PRECISION
               SNU     (output) COMPLEX*16  The  desired  unitary
               matrix U.

     CSV       (output) DOUBLE PRECISION
               SNV     (output) COMPLEX*16  The  desired  unitary
               matrix V.

     CSQ       (output) DOUBLE PRECISION
               SNQ     (output) COMPLEX*16  The  desired  unitary
               matrix Q.

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