Provided by: liblapack-doc_3.12.0-3build1_all 
NAME
lagv2 - lagv2: 2x2 generalized Schur factor
SYNOPSIS
Functions
subroutine dlagv2 (a, lda, b, ldb, alphar, alphai, beta, csl, snl, csr, snr)
DLAGV2 computes the Generalized Schur factorization of a real 2-by-2 matrix pencil
(A,B) where B is upper triangular.
subroutine slagv2 (a, lda, b, ldb, alphar, alphai, beta, csl, snl, csr, snr)
SLAGV2 computes the Generalized Schur factorization of a real 2-by-2 matrix pencil
(A,B) where B is upper triangular.
Detailed Description
Function Documentation
subroutine dlagv2 (double precision, dimension( lda, * ) a, integer lda, double precision,
dimension( ldb, * ) b, integer ldb, double precision, dimension( 2 ) alphar, double
precision, dimension( 2 ) alphai, double precision, dimension( 2 ) beta, double precision
csl, double precision snl, double precision csr, double precision snr)
DLAGV2 computes the Generalized Schur factorization of a real 2-by-2 matrix pencil (A,B)
where B is upper triangular.
Purpose:
DLAGV2 computes the Generalized Schur factorization of a real 2-by-2
matrix pencil (A,B) where B is upper triangular. This routine
computes orthogonal (rotation) matrices given by CSL, SNL and CSR,
SNR such that
1) if the pencil (A,B) has two real eigenvalues (include 0/0 or 1/0
types), then
[ a11 a12 ] := [ CSL SNL ] [ a11 a12 ] [ CSR -SNR ]
[ 0 a22 ] [ -SNL CSL ] [ a21 a22 ] [ SNR CSR ]
[ b11 b12 ] := [ CSL SNL ] [ b11 b12 ] [ CSR -SNR ]
[ 0 b22 ] [ -SNL CSL ] [ 0 b22 ] [ SNR CSR ],
2) if the pencil (A,B) has a pair of complex conjugate eigenvalues,
then
[ a11 a12 ] := [ CSL SNL ] [ a11 a12 ] [ CSR -SNR ]
[ a21 a22 ] [ -SNL CSL ] [ a21 a22 ] [ SNR CSR ]
[ b11 0 ] := [ CSL SNL ] [ b11 b12 ] [ CSR -SNR ]
[ 0 b22 ] [ -SNL CSL ] [ 0 b22 ] [ SNR CSR ]
where b11 >= b22 > 0.
Parameters
A
A is DOUBLE PRECISION array, dimension (LDA, 2)
On entry, the 2 x 2 matrix A.
On exit, A is overwritten by the ``A-part'' of the
generalized Schur form.
LDA
LDA is INTEGER
THe leading dimension of the array A. LDA >= 2.
B
B is DOUBLE PRECISION array, dimension (LDB, 2)
On entry, the upper triangular 2 x 2 matrix B.
On exit, B is overwritten by the ``B-part'' of the
generalized Schur form.
LDB
LDB is INTEGER
THe leading dimension of the array B. LDB >= 2.
ALPHAR
ALPHAR is DOUBLE PRECISION array, dimension (2)
ALPHAI
ALPHAI is DOUBLE PRECISION array, dimension (2)
BETA
BETA is DOUBLE PRECISION array, dimension (2)
(ALPHAR(k)+i*ALPHAI(k))/BETA(k) are the eigenvalues of the
pencil (A,B), k=1,2, i = sqrt(-1). Note that BETA(k) may
be zero.
CSL
CSL is DOUBLE PRECISION
The cosine of the left rotation matrix.
SNL
SNL is DOUBLE PRECISION
The sine of the left rotation matrix.
CSR
CSR is DOUBLE PRECISION
The cosine of the right rotation matrix.
SNR
SNR is DOUBLE PRECISION
The sine of the right rotation matrix.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Contributors:
Mark Fahey, Department of Mathematics, Univ. of Kentucky, USA
subroutine slagv2 (real, dimension( lda, * ) a, integer lda, real, dimension( ldb, * ) b,
integer ldb, real, dimension( 2 ) alphar, real, dimension( 2 ) alphai, real, dimension( 2
) beta, real csl, real snl, real csr, real snr)
SLAGV2 computes the Generalized Schur factorization of a real 2-by-2 matrix pencil (A,B)
where B is upper triangular.
Purpose:
SLAGV2 computes the Generalized Schur factorization of a real 2-by-2
matrix pencil (A,B) where B is upper triangular. This routine
computes orthogonal (rotation) matrices given by CSL, SNL and CSR,
SNR such that
1) if the pencil (A,B) has two real eigenvalues (include 0/0 or 1/0
types), then
[ a11 a12 ] := [ CSL SNL ] [ a11 a12 ] [ CSR -SNR ]
[ 0 a22 ] [ -SNL CSL ] [ a21 a22 ] [ SNR CSR ]
[ b11 b12 ] := [ CSL SNL ] [ b11 b12 ] [ CSR -SNR ]
[ 0 b22 ] [ -SNL CSL ] [ 0 b22 ] [ SNR CSR ],
2) if the pencil (A,B) has a pair of complex conjugate eigenvalues,
then
[ a11 a12 ] := [ CSL SNL ] [ a11 a12 ] [ CSR -SNR ]
[ a21 a22 ] [ -SNL CSL ] [ a21 a22 ] [ SNR CSR ]
[ b11 0 ] := [ CSL SNL ] [ b11 b12 ] [ CSR -SNR ]
[ 0 b22 ] [ -SNL CSL ] [ 0 b22 ] [ SNR CSR ]
where b11 >= b22 > 0.
Parameters
A
A is REAL array, dimension (LDA, 2)
On entry, the 2 x 2 matrix A.
On exit, A is overwritten by the ``A-part'' of the
generalized Schur form.
LDA
LDA is INTEGER
THe leading dimension of the array A. LDA >= 2.
B
B is REAL array, dimension (LDB, 2)
On entry, the upper triangular 2 x 2 matrix B.
On exit, B is overwritten by the ``B-part'' of the
generalized Schur form.
LDB
LDB is INTEGER
THe leading dimension of the array B. LDB >= 2.
ALPHAR
ALPHAR is REAL array, dimension (2)
ALPHAI
ALPHAI is REAL array, dimension (2)
BETA
BETA is REAL array, dimension (2)
(ALPHAR(k)+i*ALPHAI(k))/BETA(k) are the eigenvalues of the
pencil (A,B), k=1,2, i = sqrt(-1). Note that BETA(k) may
be zero.
CSL
CSL is REAL
The cosine of the left rotation matrix.
SNL
SNL is REAL
The sine of the left rotation matrix.
CSR
CSR is REAL
The cosine of the right rotation matrix.
SNR
SNR is REAL
The sine of the right rotation matrix.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Contributors:
Mark Fahey, Department of Mathematics, Univ. of Kentucky, USA
Author
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