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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Computing 40 (1988), S. 29-50 
    ISSN: 1436-5057
    Keywords: Primary 65N10 ; 65N30 ; Elliptic problems ; singularity problems ; finite element methods ; Ritz-Galerkin methods ; combined methods ; nonconforming combinations ; penalty combined methods ; simplified hybridcombined methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es werden Koppelungstechniken zwischen der Ritz-Galerkin- und der Lagrange-Finite-Elemente-Methode der Ordnungk≥1 vorgestellt, die aus einer Kombination von hybriden Techniken und Straffunktionstechniken bestehen. Mit ihrer Hilfe werden komplizierte Probleme bei homogenen und inhomogenen elliptischen Gleichungen gelöst, insbesondere mit Singularitäten oder auf unbeschränkten Bereichen. Für die numerischen Lösungen werden optimale Konvergenzraten in Sobolev-Normen bewiesen. Diese theoretischen Ergebnisse werden in numerischen Experimenten für die singuläre Motz-Gleichung verifiziert.
    Notes: Abstract The coupling techniques of simplified hybrid plus penalty functions are first presented for matching the Ritz-Galerkin method and thek(k〉-1)-order Lagrange finite element methods to solve complicated problems of elliptic equations, homogeneous or nonhomogeneous, in particular with singularities or unbounded domains. Optimal convergence rates of numerical solutions have been proved in the Sobolev norms. Moreover, the theoretical results obtained in this paper have been verified by numerical experiments for the singular Motz problem.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Computing 45 (1990), S. 311-319 
    ISSN: 1436-5057
    Keywords: 1980 Mathematics Subject Classification (1985 Revision) ; Primary 65N10 ; 65N30 ; Coupling strategy ; combined methods ; singularity problems ; interface problems ; elliptic equation ; error analysis ; stability analysis ; optimal rate of convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Zur Lösung elliptischer Randwert probleme mit Singularitäten haben wir kombinierte Methoden vorgeschlagen, die aus der Ritz-Galerkin-Methode mit singulären (oder analytischen) Basisfunktionen für einen TeilS 2 des LösungsraumesS, in dem es singuläre Punkte gibt, und aus der Finite-Elemente-Methode für den restlichen TeilS 1 vonS, wo die Lösung genügend glatt ist, bestehen. In dieser Arbeit werden allgemeine Ansätze, die zusätzliche Integrale verwenden, präsentiert, um verschiedene numerische Methoden längs ihres gemeinsamen Randes Г0 zu verbinden. Fehler und Stabilitätsuntersuchungen für eine solche allgemeine Kombinationsstrategie werden angegeben. Diese Untersuchungen sind wichtig, da sie eine theoretische Grundlage für eine Reihe von Kombinationen zwischen der Ritz-Galerkin-Methode und der Finite-Elemente-Methode bilden, die in [7] angegeben werden, und weil sie zu neuen Kombinationen von anderen analogen Methoden führen können. Außerdem können die Untersuchungen dieser Arbeit angewendet und erweitert werden, um allgemeine elliptische Randwert probleme mit Winkel-Singularitäten, Oberflächen-Singularitäten oder unbeschränkten Gebieten zu lösen.
    Notes: Abstract For solving elliptic boundary value problems with singularities, we have proposed the combined methods consisting of the Ritz-Galerkin method using singular (or analytic) basic functions for one part,S 2, of the solution domainS, where there exist singular points, and the finite element method for the remaining partS 1 ofS, where the solution is smooth enough. In this paper, general approaches using additional integrals are presented to match different numerical methods along their common boundary Г0. Errors and stability analyses are provided for such a general coupling strategy. These analyses are important because they form a theoretical basis for a number of combinations between the Ritz-Galerkin and finite element methods addressed in [7], and because they can lead to new combinations of other methods, such as the combined methods of the Ritz-Galerkin and finite difference methods. Moreover, the analyses in this paper can be applied or extended to solve general elliptic boundary value problems with angular singularities, interface singularity or unbounded domain.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Computing 44 (1990), S. 305-329 
    ISSN: 1436-5057
    Keywords: 65N10 ; 65N30 ; Automatic mesh generation ; finite element analysis ; advancing-fron method ; modified advancing-fron method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Die Anwendung des Verfahrens der Finiten Elemente im Ingenieurwesen umfaßt drei Schritte: Die Diskretisierung des Bereichs, die Gleichungsauflösung und die Fehleranalyse. Die Bereichsdiskretisierung oder Netzgeneriezung spielt als Vorläufer-Schritt eine wichtige Rolle für die Erzielung genauer Ergebnisse. In dieser Arbeit wird eine vielversprechende Technik zur Generierung zweidimensionaler Netze weiter verbessert. Unser Vorgehen erweist sich einigen derzeit verfügbaren Netzgeneratoren überlegen.
    Notes: Abstract The finite element analysis in engineering applications comprises three phases: domain discretization, equation solving and error analysis. The domain discretization or mesh generation is the pre-processing phase which plays an important role in the achievement of accurate solutions. In this paper, the improvement of one particularly promising technique for generating two-dimensional meshes is presented. Our technique shows advantages and efficiency over some currently available mesh generators.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    BIT 25 (1985), S. 70-75 
    ISSN: 1572-9125
    Keywords: E.1 [Data]: Data Structures — arrays, lists ; F.2.2 [Analysis of Algorithms and Problem Complexity]: Nonnumerical-Algorithms and Problems — sorting and searching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract For almost twenty years, the Ford-Johnson algorithm for sortingt items using comparisons was believed to be optimal. Recently, Manacher was able to show that the Ford-Johnson algorithm is not optimal for certain ranges of values oft. In this paper, we present some new algorithms which achieve much stronger results compared to Manacher's algorithms.
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  • 5
    ISSN: 1572-9125
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A third orderA-stable Rosenbrock method with built-in error estimate is developed by modifying an idea of J. R. Cash. Comparative tests are presented.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    BIT 22 (1982), S. 454-462 
    ISSN: 1572-9125
    Keywords: Merging ; Hwang-Lin merging algorithm ; binary merge algorithm ; analysis of algorithms ; 5.25 ; 5.31
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we are concerned with the merging of two linearly-ordered listsA andB consisting of elements:a 1〈a 2〈...〈b n . The Hwang-Lin merging algorithm was considered very efficient for merging two lists of arbitrary sizes. Recently, Manacher was able to develop methods which reduce the number of pairwise comparisons required in the Hwang-Lin algorithm by a factor 31/336m. We develop in this paper a new method which further improves this factor to 52/336m. It is possible that even larger improvements could be achieved.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    BIT 23 (1983), S. 409-428 
    ISSN: 1572-9125
    Keywords: Optimal merging ; top down approach ; heuristic approach
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Efficient algorithms are given to find the maximum lengthn of an ordered list in which 4 elements can be merged using exactlyk comparisons. A top down algorithm for the (2,n) merge problem is discussed and is shown to obtain the optimal merge length first reported by Hwang and Lin. Our algorithms combine this top down approach and strong heuristics, some of which derived from Hwang's optimal algorithm for the (3,n) problem, and produce a lengthn which is close to the optimal lengthf 4(k).
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    BIT 30 (1990), S. 156-160 
    ISSN: 1572-9125
    Keywords: AMS (MOS): 65L20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Contractivity is a desirable property of numerical integration methods for stiff systems of ordinary differential equations. In this paper, numerical parameters are used to allow a direct and quantitative comparison of the contractivity properties of various methods for non-linear stiff problems. Results are provided for popular Rosenbrock methods and some more recently developed semi-implicit methods.
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  • 9
    ISSN: 1436-5057
    Keywords: 65L05 ; Rosenbrock methods ; semi-implicit Runge-Kutta methods ; Richardson extrapolation ; embedding technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung In [16] werden Rosenbrockmethoden der Ordnung 4 untersucht, die zur Schrittweitensteuerung eine eingebettete Methode der Ordnung 3 verwenden. In dieser Arbeit werden neue solche Methoden hergeleitet, die auf Schrittweitensteuerung durch Richardsonextrapolation zugeschnitten sind, und beide Techniken miteinander verglichen. Es zeigt sich, daß im Gegensatz zur üblichen Meinung Extrapolation nicht schlechter ist als Einbettung. Die numerischen Ergebnisse für die 25 Beispiele aus STIFF DETEST und einige schwierigere Beispiele zeigen folgendes Verhalten: Für niedrige Genauigkeiten (∼10−2) sind eingebettete Methoden vorteilhaft, für mittlere Genauigkeiten (∼10−4) sind beide Techniken gleichwertig und für hohe Genauigkeiten (〈10−5) ist Extrapolation überlegen. Unter bestimmten Voraussetzungen kann der extrapolierte Wert als Startwert für den nächsten Schritt verwendet werden.
    Notes: Abstract In [16], Rosenbrock methods of order four are investigated using an embedded method of order three for step size control. Here, we study such a method using Richardson extrapolation for step size control and compare the two techniques with each other. The usual belief that extrapolation is inferior to embedding is not true. Numerical results for the 25 examples of STIFF DETEST and for some more difficult problems show the following behaviour: For low tolerances (∼10−2) embedding is superior, for moderate tolerances (∼10−4) both techniques are comparable and for high tolerances (〈10−5) extrapolation is superior. Under certain conditions the extrapolated value can be used for step continuation without stability problems.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of intelligent and robotic systems 8 (1993), S. 173-200 
    ISSN: 1573-0409
    Keywords: Formal specification ; robot kinematics ; VDM ; intelligent systems ; verification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Intelligent robots are autonomous and are used in environments where human interaction is hazardous or impossible. Verification of software for intelligent robots is mandatory because in situations where intelligent robots are employed online, error recovery is almost impossible. In this paper, we provide a formal framework for offline verification of software used in robotic applications. The specification enables one to design a robotic agent which represents a class of real-life robots. Forward and inverse kinematic operations of the robotic agent are specified using the specification for rigid solids and their primitive operations. An object-oriented design of the robotic agent derived from the specifications is given. We use the specification technique VDM for our purpose.
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