SRC/dlagv2.f(3)

NAME
SRC/dlagv2.f

SYNOPSIS

  Functions/Subroutines
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.

Function/Subroutine 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

Definition at line 155 of file dlagv2.f.

Author

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