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