DLARTG
November 2006
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.
[ 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.
This version has a few statements commented out for thread safety (machine parameters are computed on each entry). 10 feb 03, SJH. |