dlanv2(3)

NAME

SUBROUTINE DLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS,
SN )
    DOUBLE         PRECISION A, B, C, CS, D,  RT1I,  RT1R,
RT2I, RT2R, SN

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.

A (input/output) DOUBLE PRECISION: B (input/output) DOUBLE PRECISION C; (input/output) DOUBLE PRECISION D (input/output) DOUBLE; PRECISION On entry, the elements of the input matrix. On exit,; they are overwritten by the elements of the standardised Schur; form.
RT1R (output) DOUBLE PRECISION: RT1I (output) DOUBLE PRECISION RT2R (output); DOUBLE PRECISION RT2I (output) DOUBLE PRECISION The real and; imaginary parts of the eigenvalues. If the eigenvalues are a com; plex conjugate pair, RT1I > 0.
CS (output) DOUBLE PRECISION: SN (output) DOUBLE PRECISION Parameters of; the rotation matrix.

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).
LAPACK version 3.0 15 June 2000