SLANV2 - compute the Schur factorization of a real 2-by-2
nonsymmetric matrix in standard form
SYNOPSIS
SUBROUTINE SLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS,
SN )
REAL A, B, C, CS, D, RT1I, RT1R, RT2I, RT2R,
SN
PURPOSE
SLANV2 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.
ARGUMENTS
A (input/output) REAL
B (input/output) REAL C (input/output)
REAL D (input/output) REAL On entry, the
elements of the input matrix. On exit, they are
overwritten by the elements of the standardised
Schur form.
RT1R (output) REAL
RT1I (output) REAL RT2R (output) REAL RT2I
(output) REAL The real and imaginary parts of the
eigenvalues. If the eigenvalues are a complex con
jugate pair, RT1I > 0.
CS (output) REAL
SN (output) REAL Parameters of the rotation
matrix.
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 possi
ble, that abs(RT1R) >= abs(RT2R).
Man(1) output converted with
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