DLARTGS
Purpose
DLARTGS generates a plane rotation designed to introduce a bulge in
Golub-Reinsch-style implicit QR iteration for the bidiagonal SVD
problem. X and Y are the top-row entries, and SIGMA is the shift.
The computed CS and SN define a plane rotation satisfying
[ CS SN ] . [ X^2 - SIGMA ] = [ R ],
[ -SN CS ] [ X * Y ] [ 0 ]
with R nonnegative. If X^2 - SIGMA and X * Y are 0, then the
rotation is by PI/2.
Golub-Reinsch-style implicit QR iteration for the bidiagonal SVD
problem. X and Y are the top-row entries, and SIGMA is the shift.
The computed CS and SN define a plane rotation satisfying
[ CS SN ] . [ X^2 - SIGMA ] = [ R ],
[ -SN CS ] [ X * Y ] [ 0 ]
with R nonnegative. If X^2 - SIGMA and X * Y are 0, then the
rotation is by PI/2.
Arguments
| X |
(input) DOUBLE PRECISION
The (1,1) entry of an upper bidiagonal matrix.
|
| Y |
(input) DOUBLE PRECISION
The (1,2) entry of an upper bidiagonal matrix.
|
| SIGMA |
(input) DOUBLE PRECISION
The shift.
|
| CS |
(output) DOUBLE PRECISION
The cosine of the rotation.
|
| SN |
(output) DOUBLE PRECISION
The sine of the rotation.
|