ESMF_DLANV2 Subroutine

subroutine ESMF_DLANV2(A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN)

\brief \b ESMF_DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form. \htmlonly Download ESMF_DLANV2 + dependencies [TGZ] [ZIP] [TXT] \endhtmlonly \par Purpose:

\verbatim

ESMF_DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form:

 [ A  B ] = [ CS -SN ] [ AA  BB ] [ CS  SN ]
 [ C  D ]   [ SN  CS ] [ CC  DD ] [-SN  CS ]

where either 1) CC = 0 so that AA and DD are real eigenvalues of the matrix, or 2) AA = DD and BBCC < 0, so that AA + or - sqrt(BBCC) are complex conjugate eigenvalues. \endverbatim \param[in,out] A \verbatim A is DOUBLE PRECISION \endverbatim

\param[in,out] B \verbatim B is DOUBLE PRECISION \endverbatim

\param[in,out] C \verbatim C is DOUBLE PRECISION \endverbatim

\param[in,out] D \verbatim D is DOUBLE PRECISION On entry, the elements of the input matrix. On exit, they are overwritten by the elements of the standardised Schur form. \endverbatim

\param[out] RT1R \verbatim RT1R is DOUBLE PRECISION \endverbatim

\param[out] RT1I \verbatim RT1I is DOUBLE PRECISION \endverbatim

\param[out] RT2R \verbatim RT2R is DOUBLE PRECISION \endverbatim

\param[out] RT2I \verbatim RT2I is DOUBLE PRECISION The real and imaginary parts of the eigenvalues. If the eigenvalues are a complex conjugate pair, RT1I > 0. \endverbatim

\param[out] CS \verbatim CS is DOUBLE PRECISION \endverbatim

\param[out] SN \verbatim SN is DOUBLE PRECISION Parameters of the rotation matrix. \endverbatim \author Univ. of Tennessee \author Univ. of California Berkeley \author Univ. of Colorado Denver \author NAG Ltd. \date December 2016 \ingroup doubleOTHERauxiliary \par Further Details:

\verbatim

Modified by V. Sima, Research Institute for Informatics, Bucharest, Romania, to reduce the risk of cancellation errors, when computing real eigenvalues, and to ensure, if possible, that abs(RT1R) >= abs(RT2R). \endverbatim

Arguments