dlags2(3S)

NAME
     DLAGS2 - compute 2-by-2 orthogonal 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 )  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' denotes the transpose of
     Z

SYNOPSIS
     SUBROUTINE DLAGS2( UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV,
                        CSQ, SNQ )

         LOGICAL        UPPER

         DOUBLE         PRECISION A1, A2, A3, B1, B2, B3, CSQ, CSU, CSV, SNQ,
                        SNU, SNV

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     DLAGS2 computes 2-by-2 orthogonal 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 ) 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' denotes the transpose of Z.


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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE PRECISION The desired orthogonal matrix
             U.

     CSV     (output) DOUBLE PRECISION
             SNV     (output) DOUBLE PRECISION The desired orthogonal matrix
             V.

     CSQ     (output) DOUBLE PRECISION
             SNQ     (output) DOUBLE PRECISION The desired orthogonal matrix
             Q.

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

     This man page is available only online.