LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
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dlanv2.f File Reference

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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 
)

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

Download DLANV2 + dependencies [TGZ] [ZIP] [TXT]
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:
[in,out]A
          A is DOUBLE PRECISION
[in,out]B
          B is DOUBLE PRECISION
[in,out]C
          C is DOUBLE PRECISION
[in,out]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.
[out]RT1R
          RT1R is DOUBLE PRECISION
[out]RT1I
          RT1I is DOUBLE PRECISION
[out]RT2R
          RT2R is DOUBLE PRECISION
[out]RT2I
          RT2I is DOUBLE PRECISION
          The real and imaginary parts of the eigenvalues. If the
          eigenvalues are a complex conjugate pair, RT1I > 0.
[out]CS
          CS is DOUBLE PRECISION
[out]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.

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