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---
:name: dlanv2
:md5sum: c7c0b03a8957e1ba328eea9560c78752
:category: :subroutine
:arguments:
- a:
:type: doublereal
:intent: input/output
- b:
:type: doublereal
:intent: input/output
- c:
:type: doublereal
:intent: input/output
- d:
:type: doublereal
:intent: input/output
- rt1r:
:type: doublereal
:intent: output
- rt1i:
:type: doublereal
:intent: output
- rt2r:
:type: doublereal
:intent: output
- rt2i:
:type: doublereal
:intent: output
- cs:
:type: doublereal
:intent: output
- sn:
:type: doublereal
:intent: output
:substitutions: {}
:fortran_help: " SUBROUTINE DLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN )\n\n\
* Purpose\n\
* =======\n\
*\n\
* DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric\n\
* matrix in standard form:\n\
*\n\
* [ A B ] = [ CS -SN ] [ AA BB ] [ CS SN ]\n\
* [ C D ] [ SN CS ] [ CC DD ] [-SN CS ]\n\
*\n\
* where either\n\
* 1) CC = 0 so that AA and DD are real eigenvalues of the matrix, or\n\
* 2) AA = DD and BB*CC < 0, so that AA + or - sqrt(BB*CC) are complex\n\
* conjugate eigenvalues.\n\
*\n\n\
* Arguments\n\
* =========\n\
*\n\
* A (input/output) DOUBLE PRECISION\n\
* B (input/output) DOUBLE PRECISION\n\
* C (input/output) DOUBLE PRECISION\n\
* D (input/output) DOUBLE PRECISION\n\
* On entry, the elements of the input matrix.\n\
* On exit, they are overwritten by the elements of the\n\
* standardised Schur form.\n\
*\n\
* RT1R (output) DOUBLE PRECISION\n\
* RT1I (output) DOUBLE PRECISION\n\
* RT2R (output) DOUBLE PRECISION\n\
* RT2I (output) DOUBLE PRECISION\n\
* The real and imaginary parts of the eigenvalues. If the\n\
* eigenvalues are a complex conjugate pair, RT1I > 0.\n\
*\n\
* CS (output) DOUBLE PRECISION\n\
* SN (output) DOUBLE PRECISION\n\
* Parameters of the rotation matrix.\n\
*\n\n\
* Further Details\n\
* ===============\n\
*\n\
* Modified by V. Sima, Research Institute for Informatics, Bucharest,\n\
* Romania, to reduce the risk of cancellation errors,\n\
* when computing real eigenvalues, and to ensure, if possible, that\n\
* abs(RT1R) >= abs(RT2R).\n\
*\n\
* =====================================================================\n\
*\n"
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