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An application of the Kato-temple inequality on matrix eigenvalues to the dqds algorithm for singular values. (English) Zbl 1416.65099
The differential quotient difference with shifts (dqds) algorithm can be used to compute the singular values of a matrix with a high relative accuracy (see [K. V. Fernando and B. N. Parlett, Numer. Math. 67, No. 2, 191–229 (1994; Zbl 0814.65036)]). This is important because the sizes of singular values of a matrix may range over many orders and so high absolute accuracy may give poor results for the smaller singular values. The algorithm described in the paper above involves shifts at each stage; the implementation DLASQ of dqds in LAPACK uses what is called the aggressive strategy to choose this shift. In the present paper the authors present an alternative strategy using eigenvalue estimates to choose the shifts to implement the dqds algorithm. They give details of computer experiments for $$n\times n$$ matrices with $$n$$ ranging from $$10^{4}$$ to $$10^{6}$$ and show that often, without loss in accuracy, an implementation of their shift strategy is faster than DLASQ with the aggressive strategy.

##### MSC:
 65F15 Numerical computation of eigenvalues and eigenvectors of matrices 15A18 Eigenvalues, singular values, and eigenvectors 65F30 Other matrix algorithms (MSC2010)
##### Keywords:
singular values; dqds algorithm; shift strategy; implementation
DLASQ; LAPACK
Full Text:
##### References:
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