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  • 1995-1999  (1)
  • 1975-1979  (1)
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  • 1
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir besprechen mehrere Varianten des konjugierten Gradienten-Algorithmus unter Hervorhebung der Parameterbestimmung ohne Minimierung entlang von Linien und der Konvergenzbeschleunigung durch Zerlegung. Die hier verwendeten Zerlegungen sind dem nichtlinearen SSOR-Algorithmus verwandt. Das Verhalten der Methoden wird illustriert an der Diskretisierung eines nichtlinearen elliptischen partiellen Randwertproblems, nämlich der Minimalflächen-Gleichung. Wir entwickeln auch einen konjugierten Gradienten-Algorithmus mit Zerlegungen für Minimierung mit von oben und unten beschränkten Variabeln; ferner zeigen wir eine Anwendung der Methode auf das Hindernisproblem bei der Minimalflächen-Gleichung.
    Notes: Abstract Several variants of the conjugate gradient algorithm are discussed with emphasis on determining the parameters without performing line searches and on using splitting techniques to accelerate convergence. The splittings used here are related to the nonlinear SSOR algorithm. The behavior of the methods is illustrated on a discretization of a nonlinear elliptic partial differential boundary value problem, the minimal surface equation. A conjugate gradient algorithm with splittings is also developed for constrained minimization with upper and lower bounds on the variables, and the method is applied to the obstacle problem for the minimal surface equation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 83 (1999), S. 231-257 
    ISSN: 0945-3245
    Keywords: Mathematics Subject Classification (1991):65N22
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary. In this work we calculate the eigenvalues obtained by preconditioning the discrete Helmholtz operator with Sommerfeld-like boundary conditions on a rectilinear domain, by a related operator with boundary conditions that permit the use of fast solvers. The main innovation is that the eigenvalues for two and three-dimensional domains can be calculated exactly by solving a set of one-dimensional eigenvalue problems. This permits analysis of quite large problems. For grids fine enough to resolve the solution for a given wave number, preconditioning using Neumann boundary conditions yields eigenvalues that are uniformly bounded, located in the first quadrant, and outside the unit circle. In contrast, Dirichlet boundary conditions yield eigenvalues that approach zero as the product of wave number with the mesh size is decreased. These eigenvalue properties yield the first insight into the behavior of iterative methods such as GMRES applied to these preconditioned problems.
    Type of Medium: Electronic Resource
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