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Description

The routine 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 that satisfies the following:

with

r

nonnegative.

If

x

2

-

sigma

and

x

*

y

are 0, the rotation is by

π

/2