slags2()

subroutine slags2	(	logical	upper,
		real	a1,
		real	a2,
		real	a3,
		real	b1,
		real	b2,
		real	b3,
		real	csu,
		real	snu,
		real	csv,
		real	snv,
		real	csq,
		real	snq )

SLAGS2 computes 2-by-2 orthogonal matrices U, V, and Q, and applies them to matrices A and B such that the rows of the transformed A and B are parallel.

Download SLAGS2 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

!>
!> SLAGS2 computes 2-by-2 orthogonal matrices U, V and Q, such
!> that if ( UPPER ) then
!>
!>           U**T *A*Q = U**T *( A1 A2 )*Q = ( x  0  )
!>                             ( 0  A3 )     ( x  x  )
!> and
!>           V**T*B*Q = V**T *( B1 B2 )*Q = ( x  0  )
!>                            ( 0  B3 )     ( x  x  )
!>
!> or if ( .NOT.UPPER ) then
!>
!>           U**T *A*Q = U**T *( A1 0  )*Q = ( x  x  )
!>                             ( A2 A3 )     ( 0  x  )
!> and
!>           V**T*B*Q = V**T*( 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**T denotes the transpose of Z.
!>
!> 

Parameters

[in]	UPPER	!> UPPER is LOGICAL !> = .TRUE.: the input matrices A and B are upper triangular. !> = .FALSE.: the input matrices A and B are lower triangular. !>
[in]	A1	!> A1 is REAL !>
[in]	A2	!> A2 is REAL !>
[in]	A3	!> A3 is REAL !> On entry, A1, A2 and A3 are elements of the input 2-by-2 !> upper (lower) triangular matrix A. !>
[in]	B1	!> B1 is REAL !>
[in]	B2	!> B2 is REAL !>
[in]	B3	!> B3 is REAL !> On entry, B1, B2 and B3 are elements of the input 2-by-2 !> upper (lower) triangular matrix B. !>
[out]	CSU	!> CSU is REAL !>
[out]	SNU	!> SNU is REAL !> The desired orthogonal matrix U. !>
[out]	CSV	!> CSV is REAL !>
[out]	SNV	!> SNV is REAL !> The desired orthogonal matrix V. !>
[out]	CSQ	!> CSQ is REAL !>
[out]	SNQ	!> SNQ is REAL !> The desired orthogonal matrix Q. !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.