dlanv2.f(3)

NAME
dlanv2.f -

SYNOPSIS

  Functions/Subroutines

subroutine dlanv2 (A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN)
DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form.

Function/Subroutine Documentation

  subroutine dlanv2 (double precisionA, double precisionB, double precisionC, double precisionD, double precisionRT1R, double precisionRT1I, double precisionRT2R, double precisionRT2I, double precisionCS, double precisionSN)

DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form.

Purpose:

     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 BB*CC < 0, so that AA + or - sqrt(BB*CC) are complex
     conjugate eigenvalues.

Parameters:
    A

              A is DOUBLE PRECISION

    B

              B is DOUBLE PRECISION

    C

              C is DOUBLE PRECISION

    D

              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.

    RT1R

              RT1R is DOUBLE PRECISION

    RT1I

              RT1I is DOUBLE PRECISION

    RT2R

              RT2R is DOUBLE PRECISION

    RT2I

              RT2I is DOUBLE PRECISION
              The real and imaginary parts of the eigenvalues. If the
              eigenvalues are a complex conjugate pair, RT1I > 0.

    CS

              CS is DOUBLE PRECISION

    SN

              SN is DOUBLE PRECISION
              Parameters of the rotation matrix.

Author:
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Date:
    September 2012

Further Details:

      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).

Definition at line 128 of file dlanv2.f.

Author

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