SLAGS2(3)      LAPACK routine of NEC Numeric Library Collection      SLAGS2(3)



NAME
       SLAGS2

SYNOPSIS
       SUBROUTINE SLAGS2 (UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV,
           CSQ, SNQ)



PURPOSE
            SLAGS2 computes 2-by-2 orthogonal matrices U, V and Q, such
            that if ( UPPER ) then

                      U**T *A*Q = U**T *( A1 A2 )*Q = ( x  0  )
                                        ( 0  A3 )     ( x  x  )
            and
                      V**T*B*Q = V**T *( B1 B2 )*Q = ( x  0  )
                                       ( 0  B3 )     ( x  x  )

            or if ( .NOT.UPPER ) then

                      U**T *A*Q = U**T *( A1 0  )*Q = ( x  x  )
                                        ( A2 A3 )     ( 0  x  )
            and
                      V**T*B*Q = V**T*( B1 0  )*Q = ( x  x  )
                                      ( B2 B3 )     ( 0  x  )

            The rows of the transformed A and B are parallel, where

              U = (  CSU  SNU ), V = (  CSV SNV ), Q = (  CSQ   SNQ )
                  ( -SNU  CSU )      ( -SNV CSV )      ( -SNQ   CSQ )

            Z**T denotes the transpose of Z.




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

           A1        (input)
                     A1 is REAL

           A2        (input)
                     A2 is REAL

           A3        (input)
                     A3 is REAL
                     On entry, A1, A2 and A3 are elements of the input 2-by-2
                     upper (lower) triangular matrix A.

           B1        (input)
                     B1 is REAL

           B2        (input)
                     B2 is REAL

           B3        (input)
                     B3 is REAL
                     On entry, B1, B2 and B3 are elements of the input 2-by-2
                     upper (lower) triangular matrix B.

           CSU       (output)
                     CSU is REAL

           SNU       (output)
                     SNU is REAL
                     The desired orthogonal matrix U.

           CSV       (output)
                     CSV is REAL

           SNV       (output)
                     SNV is REAL
                     The desired orthogonal matrix V.

           CSQ       (output)
                     CSQ is REAL

           SNQ       (output)
                     SNQ is REAL
                     The desired orthogonal matrix Q.



LAPACK routine                  31 October 2017                      SLAGS2(3)