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 )

void dlags2(long upper, double a1, double a2,
double a3, double b1, double b2, double b3, double ∗csu, double ∗snu, double ∗csv, double ∗snv, double ∗csq, double ∗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.

Sun, Inc.  —  Last change: 20 Sep 1996