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On the modified Gram-Schmidt algorithm for weighted and constrained linear least squares problems
Umeå University, Faculty of Science and Technology, Departement of Computing Science.
1995 (English)In: Bit, Vol. 35, no 4, 453-468 p.Article in journal (Refereed) Published
Abstract [en]

A framework and an algorithm for using modified Gram-Schmidt for constrained and weighted linear least squares problems is presented. It is shown that a direct implementation of a weighted modified Gram-Schmidt algorithm is unstable for heavily weighted problems. It is shown that, in most cases it is possible to get a stable algorithm by a simple modification free from any extra computational costs. In particular, it is not necessary to perform reorthogonalization. Solving the weighted and constrained linear least squares problem with the presented weighted modified Gram-Schmidt algorithm is seen to be numerically equivalent to an algorithm based on a weighted Householder-like QR factorization applied to a slightly larger problem. This equivalence is used to explain the instability of the weighted modified Gram-Schmidt algorithm. If orthogonality, with respect to a weighted inner product, of the columns in Q is important then reorthogonalization can be used. One way of performing such reorthogonalization is described. Computational tests are given to show the main features of the algorithm.

Place, publisher, year, edition, pages
1995. Vol. 35, no 4, 453-468 p.
Identifiers
URN: urn:nbn:se:umu:diva-21940ISBN: 0006-3835 OAI: oai:DiVA.org:umu-21940DiVA: diva2:212197
Available from: 2009-04-21 Created: 2009-04-21 Last updated: 2009-04-21

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