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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