SLAGS2(3F)SLAGS2(3F)NAME
SLAGS2 - 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 SLAGS2( UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV,
CSQ, SNQ )
LOGICAL UPPER
REAL A1, A2, A3, B1, B2, B3, CSQ, CSU, CSV, SNQ, SNU, SNV
PURPOSE
SLAGS2 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) REAL
A2 (input) REAL A3 (input) REAL On entry, A1, A2 and A3
are elements of the input 2-by-2 upper (lower) triangular matrix
A.
B1 (input) REAL
B2 (input) REAL B3 (input) REAL On entry, B1, B2 and B3
are elements of the input 2-by-2 upper (lower) triangular matrix
B.
CSU (output) REAL
SNU (output) REAL The desired orthogonal matrix U.
CSV (output) REAL
SNV (output) REAL The desired orthogonal matrix V.
CSQ (output) REAL
SNQ (output) REAL The desired orthogonal matrix Q.
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