Previous: dlag2 Up: ../lapack-d.html Next: dlagtf

# dlags2

```
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

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 tri-
angular.
= .FALSE.: the input matrices A and B are lower tri-
angular.

A1      (input) DOUBLE PRECISION
A2      (input) DOUBLE PRECISION A3      (input)
DOUBLE PRECISION On entry, A1, A2 and A3 are entries
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 entries
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.
```