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  • 1
    Electronic Resource
    Electronic Resource
    Circulant preconditioners for Toeplitz-block matrices (1994)
    Springer
    Numerical algorithms 6 (1994), S. 89-101 
    Details
    ISSN: 1572-9265
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We propose two block preconditioners for Toeplitz-block matrices (i.e. each block is Toeplitz), intended to be used in conjunction with conjugate gradient methods. These preconditioners employ and extend existing circulant preconditioners for point Toeplitz matrices. The two preconditioners differ in whether the point circulant approximation is used once or twice, and also in the cost per step. We discuss efficient implementation of these two preconditioners, as well as some basic theoretical properties (such as preservation of symmetry and positive definiteness). We report results of numerical experiments, including an example from active noise control, to compare their performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02149764
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  • 2
    Electronic Resource
    Electronic Resource
    A composite step bi-conjugate gradient algorithm for nonsymmetric linear systems (1994)
    Springer
    Numerical algorithms 7 (1994), S. 1-16 
    Details
    ISSN: 1572-9265
    Keywords: Biconjugate gradients ; nonsymmetric linear systems ; 65N20 ; 65F10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The Bi-Conjugate Gradient (BCG) algorithm is the simplest and most natural generalization of the classical conjugate gradient method for solving nonsymmetric linear systems. It is well-known that the method suffers from two kinds of breakdowns. The first is due to the breakdown of the underlying Lanczos process and the second is due to the fact that some iterates are not well-defined by the Galerkin condition on the associated Krylov subspaces. In this paper, we derive a simple modification of the BCG algorithm, the Composite Step BCG (CSBCG) algorithm, which is able to compute all the well-defined BCG iterates stably, assuming that the underlying Lanczos process does not break down. The main idea is to skip over a step for which the BCG iterate is not defined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02141258
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  • 3
    Electronic Resource
    Electronic Resource
    A composite step conjugate gradients squared algorithm for solving nonsymmetric linear systems (1994)
    Springer
    Numerical algorithms 7 (1994), S. 17-32 
    Details
    ISSN: 1572-9265
    Keywords: Lanczos method ; conjugate gradients squared algorithm ; breakdowns ; composite step ; 65F10 ; 65F25
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We propose a new and more stable variant of the CGS method [27] for solving nonsymmetric linear systems. The method is based on squaring the Composite Step BCG method, introduced recently by Bank and Chan [1,2], which itself is a stabilized variant of BCG in that it skips over steps for which the BCG iterate is not defined and causes one kind of breakdown in BCG. By doing this, we obtain a method (Composite Step CGS or CSCGS) which not only handles the breakdowns described above, but does so with the advantages of CGS, namely, no multiplications by the transpose matrix and a faster convergence rate than BCG. Our strategy for deciding whether to skip a step does not involve any machine dependent parameters and is designed to skip near breakdowns as well as produce smoother iterates. Numerical experiments show that the new method does produce improved performance over CGS on practical problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02141259
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  • 4
    Electronic Resource
    Electronic Resource
    Additive Schwarz domain decomposition methods for elliptic problems on unstructured meshes (1994)
    Springer
    Numerical algorithms 8 (1994), S. 329-346 
    Details
    ISSN: 1572-9265
    Keywords: Unstructured meshes ; non-nested coarse meshes ; additive Schwarz algorithm ; optimal convergence rate ; 65N30 ; 65F10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We give several additive Schwarz domain decomposition methods for solving finite element problems which arise from the discretizations of elliptic problems on general unstructured meshes in two and three dimensions. Our theory requires no assumption (for the main results) on the substructures which constitute the whole domain, so each substructure can be of arbitrary shape and of different size. The global coarse mesh is allowed to be non-nested to the fine grid on which the discrete problem is to be solved and both the coarse meshes and the fine meshes need not be quasi-uniform. In this general setting, our algorithms have the same optimal convergence rate of the usual domain decomposition methods on structured meshes. The condition numbers of the preconditioned systems depend only on the (possibly small) overlap of the substructures and the size of the coares grid, but is independent of the sizes of the subdomains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02142697
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  • 5
    Electronic Resource
    Electronic Resource
    Low-rank revealing QR factorizations (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 1 (1994), S. 33-44 
    Details
    ISSN: 1070-5325
    Keywords: Rank revealing QR factorization ; Column pivoting ; Numerical rank ; Subset selection ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Rank revealing factorizations are used extensively in signal processing in connection with, for example, linear prediction and signal subspace algorithms. We present an algorithm for computing rank revealing QR factorizations of low-rank matrices. The algorithm produces tight upper and lower bounds for all the largest singular values, thus making it particularly useful for treating rank deficient problems by means of subset selection, truncated QR, etc. The algorithm is similar in spirit to an algorithm suggested earlier by Chan for matrices with a small nullity, and it can also be considered as an extension of ordinary column pivoting.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nla.1680010105
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  • 6
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    Weighted Essentially Non-oscillatory Schemes (1994)
    Elsevier
    Details
    Publication Date: 1994-11-01
    Print ISSN: 0021-9991
    Electronic ISSN: 1090-2716
    Topics: Computer Science , Physics
    Published by Elsevier
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