subroutine dlartgs (X, Y, SIGMA, CS, SN)
DLARTGS generates a plane rotation designed to introduce a bulge in implicit QR iteration for the bidiagonal SVD problem.
DLARTGS generates a plane rotation designed to introduce a bulge in implicit QR iteration for the bidiagonal SVD problem.
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.
Parameters:
X is DOUBLE PRECISION The (1,1) entry of an upper bidiagonal matrix.
Y
Y is DOUBLE PRECISION The (1,2) entry of an upper bidiagonal matrix.
SIGMA
SIGMA is DOUBLE PRECISION The shift.
CS
CS is DOUBLE PRECISION The cosine of the rotation.
SN
SN is DOUBLE PRECISION The sine of the rotation.
Author:
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
Definition at line 92 of file dlartgs.f.
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