dlags2.f File Reference

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Functions/Subroutines
subroutine	dlags2 (UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV, CSQ, SNQ)
	DLAGS2 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.

---

Function/Subroutine Documentation

subroutine dlags2	(	logical	UPPER,
		double precision	A1,
		double precision	A2,
		double precision	A3,
		double precision	B1,
		double precision	B2,
		double precision	B3,
		double precision	CSU,
		double precision	SNU,
		double precision	CSV,
		double precision	SNV,
		double precision	CSQ,
		double precision	SNQ
	)

DLAGS2 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 DLAGS2 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

 DLAGS2 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 DOUBLE PRECISION
[in]	A2	A2 is DOUBLE PRECISION
[in]	A3	A3 is DOUBLE PRECISION On entry, A1, A2 and A3 are elements of the input 2-by-2 upper (lower) triangular matrix A.
[in]	B1	B1 is DOUBLE PRECISION
[in]	B2	B2 is DOUBLE PRECISION
[in]	B3	B3 is DOUBLE PRECISION On entry, B1, B2 and B3 are elements of the input 2-by-2 upper (lower) triangular matrix B.
[out]	CSU	CSU is DOUBLE PRECISION
[out]	SNU	SNU is DOUBLE PRECISION The desired orthogonal matrix U.
[out]	CSV	CSV is DOUBLE PRECISION
[out]	SNV	SNV is DOUBLE PRECISION The desired orthogonal matrix V.
[out]	CSQ	CSQ is DOUBLE PRECISION
[out]	SNQ	SNQ is DOUBLE PRECISION The desired orthogonal matrix Q.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 152 of file dlags2.f.

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