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 precision A, double precision B, double precision C, double precision D, double precision RT1R, double precision RT1I, double precision RT2R, double precision RT2I, double precision CS, double precision SN)

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.

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 126 of file dlanv2.f.

Author

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