LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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subroutine dlartgs | ( | double precision | x, |
double precision | y, | ||
double precision | sigma, | ||
double precision | cs, | ||
double precision | sn | ||
) |
DLARTGS generates a plane rotation designed to introduce a bulge in implicit QR iteration for the bidiagonal SVD problem.
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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.
[in] | X | X is DOUBLE PRECISION The (1,1) entry of an upper bidiagonal matrix. |
[in] | Y | Y is DOUBLE PRECISION The (1,2) entry of an upper bidiagonal matrix. |
[in] | SIGMA | SIGMA is DOUBLE PRECISION The shift. |
[out] | CS | CS is DOUBLE PRECISION The cosine of the rotation. |
[out] | SN | SN is DOUBLE PRECISION The sine of the rotation. |
Definition at line 89 of file dlartgs.f.