dlanv2.f (3)

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.

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.

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