man dlartg (Fonctions bibliothèques) - generate a plane rotation so that [ CS SN ]

NAME

DLARTG - generate a plane rotation so that [ CS SN ]

SYNOPSIS

SUBROUTINE DLARTG(
F, G, CS, SN, R )
DOUBLE PRECISION CS, F, G, R, SN

PURPOSE

DLARTG generate a plane rotation so that [ CS SN ] . [ F ] = [ R ] where CS**2 + SN**2 = 1. [ -SN CS ] [ G ] [ 0 ]

This is a slower, more accurate version of the BLAS1 routine DROTG, with the following other differences:

F and G are unchanged on return.

If G=0, then CS=1 and SN=0.

If F=0 and (G .ne. 0), then CS=0 and SN=1 without doing any floating point operations (saves work in DBDSQR when there are zeros on the diagonal).

If F exceeds G in magnitude, CS will be positive.

ARGUMENTS

F (input) DOUBLE PRECISION
The first component of vector to be rotated.
G (input) DOUBLE PRECISION
The second component of vector to be rotated.
CS (output) DOUBLE PRECISION
The cosine of the rotation.
SN (output) DOUBLE PRECISION
The sine of the rotation.
R (output) DOUBLE PRECISION
The nonzero component of the rotated vector.