NAME¶

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

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

PURPOSE¶

DLAGS2 computes 2-by-2 orthogonal matrices U, V and Q, such that if ( UPPER ) then

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.