slags2(3)

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 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) REAL

A2 (input) REAL A3 (input) REAL On en

try, 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 en

try, 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 ma

trix U.

CSV (output) REAL

SNV (output) REAL The desired orthogonal ma

trix V.

CSQ (output) REAL

SNQ (output) REAL The desired orthogonal ma

trix Q.

LAPACK version 3.0 15 June 2000

SLAGS2(3)