 LAPACK  3.4.2 LAPACK: Linear Algebra PACKage
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.

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.```
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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