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dlanv2.f(3) LAPACK 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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