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  • Articles  (1,223)
  • Springer  (1,091)
  • Wiley  (132)
  • MDPI Publishing
  • 1985-1989  (1,223)
  • 1987  (1,223)
  • Computer Science  (1,223)
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  • Articles  (1,223)
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  • 1985-1989  (1,223)
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  • 1
    ISSN: 1436-5057
    Keywords: 05C99 ; 90C99 ; Polycrystals ; combinatorial optimization ; simulated annealing ; geometric probability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Viele bekannte Werkstoffe besitzen Polykristallstruktur. Derartige Strukturen können an Hand ebener Schnitte durch die Werkstoffe als Polygon-Komplexe beobachtet werden. Es wird hier die Aufgabe der Auffindung der Kanten, wenn nur die Ecken der genannten Polygon-Komplexe gegeben sind, betrachtet. Es wird eine Aufgabe der kombinatorischen Optimierung vorgeschlagen, dessen Lösung eine Approximation des Komplexes darstellt. Die Aufgabe selber wird mit der “simulierten Abkühlung” behandelt. Ermutigende erste Ergebnisse liegen vor.
    Notes: Abstract Many known materials possess polycrystalline structure. The images produced by plane cuts through such structures are polygonal complexes. The problem of finding the edges, when only the vertices of a given polygonal complex are known, is considered. A combinatorial optimization model is proposed whose solution yields an approximation of the complex. The problem itself is solved using simulated annealing. Encouraging first experiments are presented.
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  • 2
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    Computing 38 (1987), S. 13-21 
    ISSN: 1436-5057
    Keywords: 90C05 ; Linear programming ; Simplex-method ; pivot columns ; gradient criteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Im Rahmen einer Monte-Carlo-Simulationsstudie werden 31 Gradienten-Kriterien zur Auswahl der Pivotspalten beim Simplex-algorithmus getestet. Unter den dabei zugrunde gelegten Normen wird diejenige bestimmt, die bezüglich der benötigten Anzahl von Iterationsschritten und der verbrauchten Rechenzeit optimal ist. Insbesondere wird die Güte des (gebräuchlichsten) Kriteriums des steilsten Anstiegs untersucht und mit den Resultaten anderer Kriterien verglichen.
    Notes: Abstract In a Monte Carlo simulation experiment we test 31 gradient pivot choice criteria for the Simplex-method. Among the several used norms we look for the one, which is best relative to the required number of iterations and computing time. Especially the goodness of the (most used) steepest unit ascent method is analysed and compared with the results of other criteria.
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  • 3
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    Computing 38 (1987), S. 33-42 
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Ein neuer Zugang zur Herleitung optimalerB-Konvergenz wird präsentiert; optimaleB-Konvergenz der Ordnung 2 der impliziten Mittelpunktsregel und der impliziten Trapezregel sowie der Ordnung 1.5 des zweistufigen Lobatto IIIC-Verfahrens werden auf diese Weise hergeleitet.
    Notes: Abstract In this paper a new approach to derive optimalB-convergence results is presented; optimalB-convergence of order 2 for the implicit midpoint rule and the implicit trapezoidal rule and of order 1.5 for the two stage Lobatto IIIC scheme is then established.
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  • 4
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    Computing 38 (1987), S. 71-74 
    ISSN: 1436-5057
    Keywords: 65G10 ; Interval analysis ; matrix inversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Für die intervallmäßigen Schulz-Verfahren zur Einschließung der Inversen einer Matrix wird eine notwendige und eine hinreichende Bedingung für die Monotonie der Iterationsfolgen angegeben. Insbesondere wird bewiesen, daß die in [2] angegebenen Prozeduren in vielen Fällen monotones Verhalten zeigen.
    Notes: Abstract For the interval versions of Schulz's method for bounding the inverse of a matrix a necessary and a sufficient criterion for the monotonicity is derived. In particular, it is proved that the procedures given in [2] in many cases compute monotone sequences.
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  • 5
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    Computing 38 (1987), S. 75-87 
    ISSN: 1436-5057
    Keywords: 65H05 ; Complex polynomial ; zeros ; parallel Halley iteration method ; convergence order
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung In dieser Arbeit leiten wir fünf Varianten eines Algorithmus zur parallelen Bestimmung der Nullstellen eines komplexen Polynoms her. Ihre Konvergenz und deren Rate höherer Ordung werden bestimmt. Die Algorithmen werden an einem Beispiel vom Grad 10 numerisch illustriert, die Ergebnisse sind zufriedenstellend.
    Notes: Abstract In this paper we derive five kinds of algorithms for simultaneously finding the zeros of a complex polynomial. The convergence and the convergence rate with higher order are obtained. The algorithms are numerically illustrated by an example of degree 10, and the numerical results are satisfactory.
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  • 6
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    Computing 38 (1987), S. 143-161 
    ISSN: 1436-5057
    Keywords: 65H10 ; Interval arithmetic ; linear systems ; iterative methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Für Gleichungssysteme mit Intervallkoeffizienten und linearer Gestalt werden mittels geeigneter Matrixzerlegungen Iterationsverfahren eingeführt, die unter geeigneten Voraussetzungen im Vergleich zu den in [1] beschriebenen Verfahren für Gleichungssysteme in iterationsfähiger Gestalt verbesserte Konvergenzund Einschließungseigenschaften besitzen. Die Verfahren können auch im Rahmen der Lösung bestimmter nichtlinearer Gleichungssysteme mittels intervallarithmetischer Mittel verwendet werden.
    Notes: Abstract We introduce iterative methods for systems of equations with interval coefficients and linear form by suitable matrix splittings. When compared to the iterative methods for systems amenable to iteration introduced in [1], improved convergence and inclusion properties can be proved under suitable conditions. The method can also be used in the solution of specific nonlinear systems of equations by interval arithmetic methods.
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  • 7
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    Computing 38 (1987), S. 163-176 
    ISSN: 1436-5057
    Keywords: 65L05 ; stiff problems ; algorithms ; test examples ; performance criteria and evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es wird das Leistungsvermögen von Programmen betrachtet, die für die Lösung steifer Systeme gewöhnlicher Differentialgleichungen zur Verfügung stehen. Es werden drei allgemein anwendbare Algorithmen der Autoren Gear/Hindmarsh, Gottwald/Wanner und Deuflhard/Bader durch zahlreiche zufallsmäßig erzeugte Beispiele getestet, die eine beliebige Wahl der Lage und der Zahl der Eigenwerte der Jacobi-Matrix ermöglichen. Neben einer ausführlichen Auswertung der Resultate bezüglich Zuverlässigkeit und Effektivität werden Beispiele mit speziellen Eigenwertverteilungen und unterschiedlichen Strukturen der Differentialgleichungen vorgestellt und ihr Einfluß auf die Leistungsfähigkeit der Algorithmen diskutiert.
    Notes: Abstract The numerical performance of computer codes available to solve stiff systems of ODEs is evaluated. Three widely used codes of Gear/Hindmarsh, Gottwald/Wanner and Deuflhard/Bader are tested by numerous randomly generated examples which permit an arbitrary choice of the position and the number of the eigenvalues of the Jacobian. Besides a detailed evaluation of the results with regard to reliability and efficiency, examples with specified distributions of the eigenvalues and various structures of the ODEs are presented and their influence on the performance of the algorithms is discussed.
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  • 8
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    Computing 38 (1987), S. 247-259 
    ISSN: 1436-5057
    Keywords: 65 F 15 ; Eigenvalues ; Givens rotations ; fast Givens rotations ; QZ algorithm ; rounding error
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es wird dargestellt, auf welche Weise im ersten und zweiten Schritt des QZ-Algorithmus Householder-Transformationen durch schnelle Givens-Rotationen ersetzt werden können. Die Bestimmung des Rechenaufwandes für diese beiden Schritte zeigt, daß sich im ersten Schritt gegenüber dem ursprünglichen Algorithmus Operationen einsparen lassen, im zweiten Schritt jedoch nur eine unwesentliche Einsparung möglich ist. Auf Grund dieser Tatsache wird der zweite Schritt modifiziert und der daraus enstehende neue Algorithmus als FQZ-Algorithmus bezeichnet. Falls korrekt skaliert wird, entsprechen die numerischen Eigenschaften des FQZ-Algorithmus denjenigen des originalen QZ-Algorithmus.
    Notes: Abstract It is explained, how Householder reflections can be replaced by fast Givens rotations in the first and second step of the QZ algorithm. A count of the required operations for the two steps shows, that the modified first step does need less operations, but that the modified second step needs only insignificantly less operations in comparison with the original QZ algorithm. On the base of this fact a modification of the second step is proposed. The resulting new algorithm is called FQZ algorithm, which has the same numerical properties as the QZ algorithm, if a correct scaling is applied.
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  • 9
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    AI & society 1 (1987), S. 3-4 
    ISSN: 1435-5655
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
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  • 10
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    AI & society 1 (1987), S. 5-15 
    ISSN: 1435-5655
    Keywords: artificial intelligence ; social sciences ; parallel computing systems ; collaboration ; problem-solving
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Artificial intelligence is presented as a set of tools with which we can try to come to terms with human problems, and with the assistance of which, some human problems can be solved. Artificial intelligence is located in its social context, in terms of the environment within which it is developed, and the applications to which it is put. Drawing on social theory, there is consideration of the collaborative and social problem-solving processes which are involved in artificial intelligence and society. In a look ahead to the coming generations of highly parallel computing systems, it is suggested that lessons can be learnt from the highly parallel processes of human social problem-solving.
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  • 11
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    AI & society 1 (1987), S. 17-23 
    ISSN: 1435-5655
    Keywords: artificial intelligence ; intelligent program ; common-sense reasoning ; social effect ; dehumanising
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Some of the concerns people have about AI are: its misuses, effect on unemployment, and its potential for dehumanising. Contrary to what most people believe and fear, AI can lead to respect for the enormous power and complexity of the human mind. It is potentially very dangerous for users in the public domain to impute much more inferential power to computer systems, which look common-sensical, than they actually have. No matter how impressive AI programs may be, we must be aware of their limitations and should not abrogate human responsibility to such programs.
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  • 12
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    AI & society 1 (1987), S. 60-62 
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  • 13
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    AI & society 1 (1987), S. 59-59 
    ISSN: 1435-5655
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  • 14
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    AI & society 1 (1987), S. 47-58 
    ISSN: 1435-5655
    Keywords: artificial intelligence ; computer systems ; military systems ; DARPA ; natural language processing ; strategic computing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Modern weaponry is often too complex for unaided human operation, and is largely or totally controlled by computers. But modern software, particularly artificial intelligence software, exhibits such complexity and inscrutability that there are grave dangers associated with its use in non-benign applications. Recent efforts to make computer systems more accessible to military personnel through natural language processing systems, as proposed in the Strategic Computing Initiative of the Defense Advanced Research Projects Agency, increases rather than decreases the dangers of unpredictable behavior. Defense systems constitute, in fact, a paradigm case of the wrong kind of application for this technology. This cannot be expected to change, since the unpredictability stems from inherent properties of computer systems and of natural languages.
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  • 15
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    AI & society 1 (1987), S. 77-80 
    ISSN: 1435-5655
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  • 16
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    AI & society 1 (1987), S. 93-101 
    ISSN: 1435-5655
    Keywords: information technology ; knowledge ; learning ; culture history ; social anthropology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract The social sciences lack concepts and theories for an understanding of what new information technology is doing to our society. The article sketches the outlines of a broad historical and comparative approach to this issue: ‘an anthropology of information technology’. At the base is the idea ofexternalisation of knowledge as a historical process. Three main epochs are characterised by externalisation of knowledge through a) spoken language and a social organisation of specialists, b) writing and c) computer programming. The impact of expert systems on learning is also discussed.
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  • 17
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    AI & society 1 (1987), S. 85-91 
    ISSN: 1435-5655
    Keywords: artificial intelligence ; creativity ; cultural function ; resolutive intelligence ; problematic intelligence ; AI products ; piping of thought
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Over the years, AI has undergone a transformation from its original aim of producing an ‘intelligent’ machine to that of producing pragmatic solutions of problems of the market place. In doing so, AI has made a significant contribution to the debate on whether the computer is an instrument or an interlocutor. This paper discusses issues of problem solving and creativity underlying this transformation, and attempts to clarify the distinction between theresolutive intelligence andproblematic intelligence. It points out that the advance of ‘intelligent’ technology, with its failure to make a clear distinction betweenresolutive andcreative intelligence, could contribute to the further cultural marginalisation of human activities not connected with production. A further danger is that AI products may suffer a further loss of social reputation and prestige for those activities for which it is not possible to build artificial devices.
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  • 18
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    AI & society 1 (1987), S. 137-137 
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  • 19
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    AI & society 1 (1987), S. 137-137 
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  • 20
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    AI & society 1 (1987), S. 144-146 
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  • 21
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    AI & society 1 (1987), S. 138-143 
    ISSN: 1435-5655
    Keywords: class struggle ; deskilling ; division of labor ideology ; manual and intellectual labor ; worker's control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract AI is supposed to be a scientific research program for developing and analyzing computer-based systems that mimic natural psychological processes. I argue that this is a mere fiction, a convenient myth. In reality, AI is a technology for reorganizing the relations of production in workplaces, and specifically for increasing management control. The appeal of the AI myth thus serves as ideological justification for increasing managerial domination. By focusing on the AI myth, critics of AI are diverting themselves from the very important task of preventing this increasingly dangerous threat to deskill and dehumanize large sectors of the workforce.
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  • 22
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    AI & society 1 (1987), S. 25-36 
    ISSN: 1435-5655
    Keywords: dialogue ; French Age of Enlightenment ; to follow a rule ; essentially contested concepts ; propositional knowledge ; practical knowledge ; knowledge of familiarity ; epistemological error
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract A quotation from Shakespeare's play King Lear, ‘I will teach you differences’, encapsulates the spirit of this paper. The distinction is introduced between three different categories of knowledge: i) propositional knowledge, ii) skill or practical knowledge and iii) knowledge of familiarity. In the present debate on ‘Information Society’, there is a clear tendency to overemphasise the theoretical knowledge at the expense of practical knowledge thereby completely ignoring the knowledge of familiarity. It is argued that different forms of theoretical knowledge are required for the design of current computer technology and the study of the practice of computer usage. The concept of dialogue and the concept of ‘To Follow a Rule’ therefore fundamental to the understanding of the practice of computer usage.
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  • 23
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    AI & society 1 (1987), S. 103-114 
    ISSN: 1435-5655
    Keywords: artificial intelligence ; human decision making ; expert systems ; connectionism ; computer systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this paper I shall describe the symbolic search space paradigm which is the dominant model for most of AI. Coupled with the mechanisms of logic it yields the predominant methodology underlying expert systems which are the most successful application of AI technology to date. Human decision making, more precisely, expert human decision making is the function that expert systems aspire to emulate, if not surpass. Expert systems technology has not yet proved to be a decisive success — it appears to fare better in some areas of human expertise than others. As a result subdomains of human expertise are variously categorised and we shall examine a few of the suggested classification schemes. A particular line of argument explored is one which maintains that certain types of human decision making, at least, are not adequately approximated by the symbolic search space paradigm of AI. Furthermore, attempts to project this inadequate model of human decision making via implementations of expert systems will be detrimental to both our image of ourselves and the future possibilities for AI software. Finally, we examine one possible route to the realization of AI, perhaps even practical applications of AI, that is a significant alternative to the model offered by the symbolic search space paradigm.
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  • 24
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    AI & society 1 (1987), S. 137-137 
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  • 25
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    AI & society 1 (1987), S. 127-136 
    ISSN: 1435-5655
    Keywords: interactivity ; choice enablement ; the semiotic theory of indices ; intelligent video ; computer based training
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Interactive Video (IV) is now firmly established as a training tool in commerce and industry; the electronic maintenance manual is gaining ground; IV is making inroads into marketing strategies, as a point of sales device; any respectable amusement arcade will have at least one interactive video game; and of course the allied technologies of compact sound disc and CD ROM are both beginning to revolutionise their respective fields of information storage and dissemination. This paper concentrates on the specific problem of Interactive Video and its associated computing requirements in the fields of education and training, suggesting ways in which the introduction of ‘intelligence’ both artificial and human into such systems will be essential to their long-term educational and also commercial success.
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  • 26
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    AI & society 1 (1987), S. 146-150 
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  • 27
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    AI & society 1 (1987), S. 151-156 
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  • 28
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    AI & society 1 (1987), S. 157-160 
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  • 29
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    Engineering with computers 2 (1987), S. 167-183 
    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Computer modeling of mixed-mode crack propagation has rarely been attempted. This is because of the difficulty in updating the geometrical description to represent the changing crack geometry. The development of two interactive, graphical fracture propagation systems is described here. The Finite Element Fracture Analysis Program—Graphical (FEFAP-G) is a two-dimensional fracture propagation system. The BEM3D is a three-dimensional boundary element fracture propagation system. In addition, the implementation of the BEM3D analysis program in a configuration formed by an FPS-264 processor attached to a VAX-11/750 used as host computer is described. The results show that a realistic three-dimensional boundary element analysis of crack propagation is not only feasible with the aid of attached processors, but it can have its total time reduced by factors of the order of hundreds when compared to VAX alone statistics. In an example problem concerning fatigue crack propagation in a stiffened wing skin, both FEFAP-G and the BEM3D are employed to illustrate the utility of the fracture propagation systems.
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    Engineering with computers 2 (1987), S. 199-208 
    ISSN: 1435-5663
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    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract An expert consultant and teaching aid has been developed to aid users of the MSC/NASTRAN (MacNeal-Schwendler Corp, Los Angeles, CA, USA) finite element code in the modeling process with two-dimensional elements. Written in LISP and LOOPS, an object-oriented programming language, the system, known as PLASHTRAN, allows engineers to work in a natural environment to obtain modeling recommendations. The program performs efficiently, especially when iterations in design require changes in the finite element model. The easily expandable modeling framework allows the knowledge base to incorporate new information.
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    Engineering with computers 2 (1987), S. 219-238 
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    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper presents a design strategy in which structural components are designed automatically by applying three types of knowledge: knowledge in a design standard; “textbook” knowledge of structural, material, and geometrical relationships; and knowledge representing designer-dependent design expertise. The design strategy selects from the designer-dependent knowledge source the behavior limitations—limit states of an object in a given stress state—to consider, translates the behavior limitations into a subset of corresponding standard requirements, generates a set of constraints from the requirements and the relations in the knowledge-base of “textbook” relationships, satisfies the constraints, and then checks the satisfaction of all remaining applicable requirements. By using this design strategy, it is possible to construct a knowledge-based design strategy that is standard independent, so that the same design process can be performed regardless of which design standard is explicitly represented. The design strategy described has been implemented in a prototype knowledge-based system, SPEX, which has a blackboard architecture similar to, but much simpler than, that of HEARSAY. The blackboard represents the level of abstraction through which a component design progresses. The knowledge-base in SPEX consists of several knowledge sources that perform portions of the component design task. Control of the design process knowledge sources in SPEX is rule-based.
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    Engineering with computers 3 (1987), S. 21-33 
    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper presents an analytical method for acoustic forced pulsations of reciprocating compressor pipeline systems have a treelike structure that consists of an arbitrary number of branchings with optional elements—pipes, volumes, orifices, and so on. The plane wave acoustic model is used to describe the method, and the solution works by using an extended Schmidt-Kuhlmann-type approach. On the basis of a graph and matrix interpretation of the structure, a generalized algorithm is developed for determining the actual terms that describe the transfer properties of the system and to help calculate the acoustic pressure and velocity pulsations. The algorithm makes it possible to mechanize programming in the case of both natural frequency and forced pulsation calculations. The program package developed here for the personal computer can be directly applied in the design practice with success. It is also applicable to other linear systems with treelike structures.
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    Engineering with computers 3 (1987), S. 69-86 
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    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The development of an expert system for the postevent assessment of reinforced concrete structures subjected to severe loading environments, such as those that correspond to blast and shock effects, is presented and discussed. Initially, the observed behavioral aspects of the structures are presented, then a background discussion of the requirements from an expert system is given, and finally, the specific details for the present approach are examined. Examples of rules and of a typical run are presented, and the results are compared to information obtained from previous studies on the same structures.
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    Engineering with computers 3 (1987), S. 87-99 
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    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Extracting information about contact between two convex bodies from the measured force vector is a prerequisite for any fine compliant motion control strategy. Contact information contains the direction and orientation of the contact surface normal and its relative location and orientation with respect to the compliant reference frame system. A method for interpreting the contact force feedback during compliant robot motion control, using kinematic screws, is presented. Domain specific rules combined with partial a priori knowledge of mating parts geometry and interpreted force signals are used to reason and make inferences about the initial contact configuration. The likely contact surfaces are predicted and point(s) or line(s) of contact are fully defined. These surfaces are idealized and represented by quadratic equations or polyhedral surfaces. The geometric properties of surfaces at the contact location are used to select the contact configuration when multiple solutions exist. An algorithm for predicting the Expected Contact Configuration (ECC) has been developed and is illustrated here with examples. Experimental validation of the developed expert system prototype, using a 6R manipulator, a six-axis force sensor, and a host computer is described.
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  • 35
    ISSN: 1435-5663
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    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper presents a study and comparison of shape design sensitivity analysis algorithms that are based on the continuum adjoint variable method, the continuum direct differentiation method, and the finite difference method, implemented on a supermini computer with an attached array processor. The basic algorithms and their differences in evaluating shape design sensitivity coefficients are outlined. A solution method for solving a system of equations, using a general sparse storage technique, is used for numerical implementation of shape design sensitivity analysis. It is found that computing shape design sensitivity coefficients using the direct differentiation method is significantly more efficient than using the adjoint variable method or the finite difference method. A detailed performance evaluation of the methods, using an attached array processor, is presented. The performance of the attached array processor, compared to a supermini computer is shown to depend strongly on the type of computations to be carried out. When only parts of a program are running on an attached array processor, the CPU time distribution among the different subroutines of the program can change significantly, compared to using the host processor only.
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  • 36
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    Computing 38 (1987), S. 275-280 
    ISSN: 1436-5057
    Keywords: 65K05 ; 90C30 ; Interval analysis ; global maximum ; iterative method
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    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Unter Verwendung der “Bisektionsregel” von Moore wird ein Algorithmus angegeben, der eine Intervallversion der iterativen Methode von Shubert zur Bestimmung des globalen Maximums einer Funktion einer Veränderlichen auf den abgeschlossenen Intervall [a, b] darstellt. Der Algorithmus konvergiert immer; er kann leicht auf den höherdimensionalen Fall ausgedehnt werden. Er erscheint viel einfacher als der Algorithmus von Shubert und Basso, ergibt aber vergleichbare Ergebnisse.
    Notes: Abstract Using the “bisection rule” of Moore, a simple algorithm is given which is an interval version of Shubert's iterative method for seeking the global maximum of a function of a single variable defined on a closed interval [a, b]. The algorithm which is always convergent can be easily extended to the higher dimensional case. It seems much simpler than and produces results comparable to that proposed by Shubert and Basso.
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  • 37
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    Computing 38 (1987), S. 341-345 
    ISSN: 1436-5057
    Keywords: Approximation ; n-dimensional grid
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    Description / Table of Contents: Zusammenfassung Es wird ein Verfahren zur Bestimmung einer Translation eines rechtwinkeligen Gitters mit der Eigenschaft, daß eine endliche Punktmenge des ℝN möglichst gut durch Gitterpunkte approximiert wird, angegeben.
    Notes: Abstract A procedure is given for translating a rectangular grid in such a way that a finite set of points in ℝN is approximated as good as possible by points of the translated grid.
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  • 38
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    Computing 38 (1987), S. 347-353 
    ISSN: 1436-5057
    Keywords: 11K45 ; 65D32 ; 65D30 ; Pseudo-random numbers ; Monte-Carlo-methods ; numerical integration ; quadrature and cubature formulas
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    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Die Berechnung der sogenannten optimalen Koeffizienten führt in höheren Dimensionen und für größere ModulenN bei Verwendung der bekannten Methoden zu praktisch, unüberwindbaren Rechenzeitproblemen. In dieser Note geben wir eine Methode zur Berechnung „nützlicher Koeffizienten” an, wobei die Berechnung dieser Koeffizienten praktisch keine Rechenzeit für beliebige Dimensionens und beliebige ModulenN benötigt. Während die theoretische Wirksamkeit dieser „nützlichen Koeffizienten” etwa nur die Hälfte der Effizienz der bestmöglichen Koeffizienten beträgt, deuten alle praktischen Tests darauf hin, daß unsere Methode ebenfalls zu optimaler Effizienz führt. Eine Reihe von numerischen Experimenten unter Benutzung der „nützlichen Koeffizienten” und der optimalen Koeffizienten wird wiedergegeben.
    Notes: Abstract The computation of optimal coefficients for higher dimensionss and larger modulesN by means of the methods known hitherto leads to practically insurmountable problems regarding the computing time needed. In this note we give a method for computing “useful coefficients”, where the computation of these coefficients is immediate and where the computing time is practically negligible for anys andN. Whereas the theoretical efficiency of those “useful coefficients” is roughly speaking half the efficiency of the best possible coefficients, all practical tests indicate that our methods lead to optimal performance as well. A series of computational comparisons between the “useful coefficients” and the optimal ones is enclosed.
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  • 39
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    Computing 39 (1987), S. 19-26 
    ISSN: 1436-5057
    Keywords: 15A57 ; 65F30 ; Hankel matrix ; Stieltjes moment problem ; stability of real polynomials ; numerically stable definiteness test
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    Description / Table of Contents: Zusammenfassung Ein Test auf gleichzeitige Definitheit einer HankelmatrixR={r i+j } i,j N =0 und ihrer UntermatrixS={r i+j+1 } i,j N−1 =0 wird angegeben. Er ermöglicht eine Beschreibung aller Erweiterungen vonR, die die Definitheit vonR undS enthalten. Diese Beschreibung wiederum kann als Definitheitstest benutzt werden. Dieser Test zeigt eine bemerkenswerte numerische Stabilität.
    Notes: Abstract A definiteness test for a Hankel matrixR={r i+j } i,j N =0 and its lower submatrixS={r i+j+1 } i,j N−1 =0 is given. The test allows a description of all extensions ofR which preserve definiteness of bothR andS. This description in turn can be used as a definiteness test and it demonstrates a remarkable numerical stability.
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  • 40
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    Computing 39 (1987), S. 57-69 
    ISSN: 1436-5057
    Keywords: 65F15 ; 73D20 ; 15A18 ; 15A15 ; eigenvalue problem ; non-linear equations ; QR decomposition ; surface waves
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    Description / Table of Contents: Zusammenfassung Numerische Aspekte des verallgemeinerten EigenwertproblemsA μ c=0 werden untersucht, wobeiA μ eine parameterabhängige Matrix ist. Es wird empfohlen, Determinanten durch das betragskleinste Diagonalelement vonR bzw.U in derQR-bzw.LU-Zerlegung zu ersetzen. Diese Idee stammt von Kublanovskaya [7]. Das Verhalten dieses betragskleinsten Diagonalelements wird betrachtet, und mehrere numerische Verfahren werden vorgestellt und untersucht. Diese Verfahren werden bei der Berechnung akustischer Oberflächenwellen in Schichtsystemen von piezoelektrischen Substanzen angewendet, wobei sie sehr gute Ergebnisse liefern. In diesem Teil wird auch der Spezialfall betrachtet, daßA μ Matrixpolynom ist.
    Notes: Abstract Numerical aspects of the generalized eigenvalue problemA μ c=0 are discussed whereA μ is a parameter-dependent matrix. Instead of determinants, the use of the smallest diagonal element ofR resp.U in theQR resp.LU decomposition is recommended. This idea has first been used by Kublanovskaya [7]. The behaviour of this smallest diagonal element is considered, and several iterative procedures are constructed and discussed. The methods are applied to the computation of acoustic surface waves in layered systems of piezoelectric media where they prove to be powerful. In this part also the special case whenA μ is a matrix polynomial is mentioned.
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  • 41
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    Computing 39 (1987), S. 87-91 
    ISSN: 1436-5057
    Keywords: 65C10 ; 65C05 ; 68C55 ; Random number generation ; Log-concave distributions ; Rejection algorithm
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    Description / Table of Contents: Zusammenfassung Wir geben einen raschen Algorithmus an, der Zufallszahlen mit log-konkaver Verteilung (z. B. binomisch, Poisson, hypergeometrisch, negativ binomisch, geometrisch, logarithmisch, Polya-Eggenberger) erzeugt. Die mittlere Rechenzeit ist bezüglich all dieser Verteilungen gleichmäßig beschränkt. Der Algorithmus kann in wenigen Zeilen einer höheren Programmiersprache implementiert werden.
    Notes: Abstract We give a short algorithm that can be used to generate random integers with a log-concave distribution (such as the binomial, Poisson, hypergeometric, negative binomial, geometric, logarithmic series or Polya-Eggenberger distributions). The expected time is uniformly bounded over all these distributions. The algorithm can be implemented if a few lines of high level language code.
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  • 42
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    Computing 39 (1987), S. 141-153 
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    Description / Table of Contents: Zusammenfassung Es wird eine Methode zur Erzeugung von Zufallsvektoren durch Transformation gleichmäßig verteilter Vektoren vorgestellt. Die Methode wird angewandt zur Konstruktion von Algorithmen zur Erzeugungq-exponential-, mehrdimensional normal- sowie mehrdimensionalt-verteilter Vektoren.
    Notes: Abstract The paper discusses a general method of computer generation of random vectors based on transformations of uniformly distributed vectors. This method is then applied to build up efficient algorithms for generatingq-exponential random vectors and multivariate normal ort-distributed vectors. Comparisons and connections with other similar algorithms are also presented.
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  • 43
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    Computing 39 (1987), S. 175-181 
    ISSN: 1436-5057
    Keywords: 65L05 ; CR: G1.7
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    Description / Table of Contents: Zusammenfassung Die Maximalordnungp optimalerB-Konvergenz vons-stufigen Lobatto III C-Verfahren mit mehr als drei Stufen —angewandt auf Anfangswertprobleme mit negativer einseitiger Lipschitzkonstantem — wird hergeleitet; sie ists−1.
    Notes: Abstract The maximum orderp for which ans-stage Lobatto III C method,s〉-4, is optimallyB-convergent for problems with a negative one-sided Lipschitz constantm is derived; it turns out to bes−1.
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  • 44
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    Computing 39 (1987), S. 187-199 
    ISSN: 1436-5057
    Keywords: 68A05 (05C35, 05C38, 16A78, 65F05, 68E10) ; Algorithms ; design ; performance
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    Description / Table of Contents: Zusammenfassung Es wird ein orthogonales systolisches Feld (systolic array) mitn(n+1) einfachen Prozessoren entworfen, das das algebraische Wegproblem in nur 5n−2 Schritten lösen kann, im Vergleich zu 7n−2 Schritten beim hexagonalen systolischen Feld von Rote [8].
    Notes: Abstract This paper is devoted to the design of an orthogonal systolic array ofn(n+1) elementary processors which can solve any instance of the Algebraic Path Problem within only 5n−2 time steps, and is compared with the 7n−2 time steps of the hexagonal systolic array of Rote [8].
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  • 45
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    Computing 39 (1987), S. 201-217 
    ISSN: 1436-5057
    Keywords: Two-dimensional packing ; bin-packing ; heuristic algorithm ; worst-case analysis ; probabilistic analysis ; on-line algorithm
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    Description / Table of Contents: Zusammenfassung Wir geben einen neuen Näherungs-Algorithmus für das zweidimensionale Packungsproblem an. Er beruht auf zwei eindimensionalen Packungsalgorithmen. Da der Algorithmus von next-fit Typ ist, kann er auch in solchen Fällen benutzt werden, wo die Ausgabe on-line sein muß (d. h. sobald wir einen neuen Behälter eröffnen, haben wir keine Möglichkeit, Elemente in früher geöffnete Behälter zu packen). Wir geben eine gute Schranke im schlechtesten Fall an und zeigen, daß diese Schranke von der Maximalgröße der gepackten Rechtecke abhängt. Schließlich untersuchen wir noch das mittlere Verhalten des Algorithmus.
    Notes: Abstract We present a new approximation algorithm for the two-dimensional bin-packing problem. The algorithm is based on two one-dimensional bin-packing algorithms. Since the algorithm is of next-fit type it can also be used for those cases where the output is required to be on-line (e. g. if we open an new bin we have no possibility to pack elements into the earlier opened bins). We give a tight bound for its worst-case and show that this bound is a parameter of the maximal sizes of the items to be packed. Moreover, we also present a probabilistic analysis of this algorithm.
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  • 46
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    Computing 39 (1987), S. 271-279 
    ISSN: 1436-5057
    Keywords: 65B15 ; 65D20 ; 65D30 ; Triconi's psi function ; trapezoidal rule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Die Trapezregel wird zur numerischen Auswertung einer Integraldarstellung von Tricomis Psi-Funktion Ψ(a, c; x) füra, x ε ℝ+ undc ε ℝ verwendet. Die unvermutet hohe Genauigkeit wird durch eine gründliche Untersuchung des Restglieds der Euler-Maclaurin-Formel erklärt. Außerdem wird eine einfache und effektive numerische Prozedur angegeben, durch die man explizite Zahlenwerte der Psi-Funktion erhält.
    Notes: Abstract The trapezoidal rule is applied to the numerical calculation of an integral representation of Tricomi's psi function Ψ(a, c; x) fora, x ε ℝ+ andc ε ℝ. The unexpectedly high accuracy is explained by means of a careful investigation of the remainder terms of the Euler-Maclaurin formula. A simple and efficient numerical procedure for obtaining values of the psi function is given.
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  • 47
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    Computing 39 (1987), S. 307-325 
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    Description / Table of Contents: Zusammenfassung Eine neue Methode zur Lösung nichtlinearer Least-Squares-Probleme bei hochdimensionaler dünnbesetzter Jakobimatrix wird vorgestellt. Die wichtigsten Charakteristika sind: a) Die Gauß-Newton-Gleichung wird „teilweise” bei jeder Iteration gelöst, wobei eine präkonditionierte konjugierte Gradientenmethode verwendet wird. b) Die neue Lösung wird über eine zweidimensionale trust-region Technik erreicht, ähnlich der von Bulteau und Vial vorgeschlagenen Variante. Globale und lokale Konvergenzaussagen werden bewiesen und anhand einiger numerischer Beispiele demonstriert.
    Notes: Abstract We introduce a new method for solving Nonlinear Least Squares problems when the Jacobian matrix of the system is large and sparse. The main features of the new method are the following: a) The Gauss-Newton equation is “partially” solved at each iteration using a preconditioned Conjugate Gradient algorithm. b) The new point is obtained using a two-dimensional trust region scheme, similar to the one introduced by Bulteau and Vial. We prove global and local convergence results and we present some numerical experiments.
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  • 48
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    Computing 39 (1987), S. 353-362 
    ISSN: 1436-5057
    Keywords: Runge-Kutta-integration ; truncation error ; error estimates ; accumulated error ; true error ; A-stability
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    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Explizite Runge-Kutta-Formeln mit eingebauter Schätzung des globalen Diskretisierungsfehlers sind wohlbekannt. Es wird ein Vorgehen dargestellt,A-stabile und starkA-stabile Runge-Kutta-Formeln mit eingebauter Schätzung des globalen Diskretisierungsfehlers zu gewinnen.
    Notes: Abstract Explicit Runge-Kutta formulae with built-in estimates of the accumulated truncation error are well known. A method is presented for developingA-stable and stronglyA-stable Runge-Kutta algorithms with built-in estimates of the accumulated truncation error.
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  • 49
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    Computing 39 (1987), S. 327-344 
    ISSN: 1436-5057
    Keywords: 05-04 ; 05C45 ; 90C10 ; Matching ; cutting plane algorithm ; polyhedral combinatorics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir beschreiben die Implementierung eines Schnittebenenverfahrens zur Bestimmung minimaler gewichteter perfekter 2-Matchings. Der Algorithmus baut auf der vollständigen Beschreibung des perfekten 2-Matching-Polytops, die Edmonds angegeben hat, auf und verwendet die Simplexmethode zur Lösung der im Verfahren auftretenden LP-Relaxierungen. Schnittebenen werden entweder mit schnellen Heuristiken bestimmt, oder, falls diese nicht erfolgreich sind, mit einer effizienten und auf 2-matching-Ungleichungen abgestimmten Implementierung des Padberg-Rao-Verfahrens. Mit diesem Algorithmus konnten 2-Matching-Probleme in vollständigen Graphen mit bis zu 1000 Knoten, d. h. mit bis zu 499.500 Variablen, in weniger als einer Stunde CPU-Zeit auf einem Rechner mittlerer Leistung gelöst werden.
    Notes: Abstract We describe an implementation of a cutting plane algorithm for the minimum weight perfect 2-matching problem. This algorithm is based on Edmonds' complete description of the perfect 2-matching polytope and uses the simplex algorithm for solving the LP-relaxations coming up. Cutting planes are determined by fast heuristics, or, if these fail, by an efficient implementation of the Padberg-Rao procedure, specialized for 2-matching constraints. With this algorithm 2-matching problems on complete graphs with up to 1000 nodes (i.e., 499,500 variables) have been solved in less than 1 hour CPU time on a medium speed computer.
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  • 50
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    Computing 39 (1987), S. 363-369 
    ISSN: 1436-5057
    Keywords: 65 G 10 ; 65 H 05 ; 65 H 10 ; Interval arithmetic ; Newton's method ; order of convergence
    Source: Springer Online Journal Archives 1860-2000
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    Description / Table of Contents: Abstract It is well known that the classical Newton method is cubically convergent to a simple zero if the second derivative vanishes at the zero. We first show that this property does not hold for the interval-Newton-method. If, however, the interval arithmetic evaluation of the derivative in this method is replaced by the mean-value form or by the centered form, respectively, then the method is again cubically convergent.
    Notes: Zusammenfassung Es ist bekannt, daß das klassische Newton-Verfahren kubisch gegen eine einfache Nullstelle konvergiert, wenn die zweite Ableitung an der Nullstelle verschwindet. Wir zeigen zunächst, daß sich diese Eigenschaft nicht auf das Intervall-Newton-Verfahren überträgt. Verwendet man jedoch anstelle der intervallmäßigen Auswertung der Ableitung die Mittelwertform oder die zentrierte Form, so erhält man wieder kubische Konvergenz.
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    Computing 38 (1987), S. 23-31 
    ISSN: 1436-5057
    Keywords: 42A10 ; 65D10 ; Splines ; Bernoulli polynomials
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    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Bernoulli-Polynome und die zugehörigen Bernoulli-Funktionen sind von grundlegender Bedeutung für theoretische Untersuchungen in der numerischen Mathematik. M. Golomb und andere verwendeten die Bernoulli-Funktionen bei der Konstruktion periodischer Splines. In einer unbekannten Arbeit untersuchte U. Wegener Restglieddarstellungen für die Lagrange-Interpolation mittels Bernoulli-Funktionen. Wir verwendeten die Kernfunktion von Wegener zur Konstruktion von periodischenB-Splines. Für äquidistante Knoten zeigen wir, daß die Methode der Interpolation mittels Translation von Locher anwendbar ist auf periodischeB-Splines. Dieser Zusammenhang liefert einen einfachen und stabilen Algorithmus zur Berechnung periodischer Interpolationssplines mittels der diskreten Fourier-Transformation.
    Notes: Abstract Bernoulli polynomials and the related Bernoulli functions are of basic importance in theoretical numerical analysis. It was shown by Golomb and others that the periodic Bernoulli functions serve to construct periodic polynomial splines on uniform meshes. In an unknown paper Wegener investigated remainder formulas for polynomial Lagrange interpolation via Bernoulli functions. We will use Wegener's kernel function to construct periodicB-splines. For uniform meshes we will show that Locher's method of interpolation by translation is applicable to periodicB-splines. This yields an easy and stable algorithm for computing periodic polynomial interpolating splines of arbitrary degree on uniform meshes via discrete Fourier transform.
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  • 52
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    Computing 38 (1987), S. 43-57 
    ISSN: 1436-5057
    Keywords: 65F15 ; AMS Secondary ; 65H10 ; invariant subspace ; iterative refinement ; generalized eigenvalue problem
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    Description / Table of Contents: Zusammenfassung In diesem Bericht werden drei Verfahren von Chatelin, Dongarra/Moler/Wilkinson und Stewart für die Verbesserung von Annäherungen von invarianten Unterräumen verglichen. Durch das Wechseln von Variablen zeigen wir, daß, obwohl die drei Verfahren anscheinend unterschiedliche Gleichungen lösen, in Wirklichkeit die gleiche Gleichung gelöst wird, die Riccati-Gleichung. Diese Analyse hat drei Vorteile. Zuerst liefert sie eine gemeinsame Konvergenzbedingung, die die lineare Konvergenz der ersten zwei Verfahren garantiert, und eine etwas stärkere Bedingung für die quadratische Konvergenz des letzten Verfahrens. Zweitens führt sie zu einem Hybridverfahren mit den Vorteilen aller drei. Drittens liefert sie Verfahren und Konvergenzbedingungen für das allgemeine Eigenwertproblem. Diese Verfahren werden auch mit Verfahren verglichen, die für kontrolltheoretische Probleme benutzt werden.
    Notes: Abstract We compare three methods for refining estimates of invariant subspaces, due to Chatelin, Dongarra/Moler/Wilkinson, and Stewart. Even though these methods all apparently solve different equations, we show by changing variables that they all solve the same equation, the Riccati equation. The benefit of this point of view is threefold. First, the same convergence theory applies to all three methods, yielding a single criterion under which the last two methods converge linearly, and a slightly stronger criterion under which the first algorithm converges quadratically. Second, it suggest a hybrid algorithm combining advantages of all three. Third, it leads to algorithms (and convergence criteria) for the generalized eigenvalue problem. These techniques are compared to techniques used in the control systems community.
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  • 53
    ISSN: 1436-5057
    Keywords: 65N30 ; 65H10 ; Nonlinear radiation cooling problem ; finite element solution ; successive overrelaxation method with projection ; convergence
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    Description / Table of Contents: Zusammenfassung In dieser Arbeit betrachten wir das sukzessive Überrelaxationsverfahren mit Projektion zu finiten Elementlösungen unter nichtlinearen Radiationsrandbedingungen, insbesondere den Nachweis einer Konvergenz des sukzessiven Überrelaxationsverfahrens mit Projektion. An einigen numerischen Ergebnissen soll die Anwendbarkeit illustriert werden.
    Notes: Abstract In this paper, we consider the successive overrelaxation method with projection for obtaining the finite element solutions under the nonlinear radiation boundary conditions. In particular we establish the convergence of the successive overrelaxation method with projection. Some numerical results are also given to illustrate the usefulness.
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  • 54
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    Computing 38 (1987), S. 133-141 
    ISSN: 1436-5057
    Keywords: 65H10 ; Nonlinear systems ; Quasi-Newton methods ; sparse matrices ; factorization of matrices
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    Description / Table of Contents: Zusammenfassung Wir stellen in dieser Arbeit ein Verfahren vom Quasi-Newton-Typ für große, dünnbesetzte nichtlineare Gleichungssysteme vor, das die QR-Faktorisierung der näherungsweisen Jacobi-Matrix benutzt. Das Verfahren gehört zu einer allgemeinen Klasse von Algorithmen, für die wir die lokale Konvergenz beweisen. Einige numerische Experimente deuten auf die Verläßlichkeit des neuen Algorithmus hin.
    Notes: Abstract In this paper we present a Quasi-Newton type method, which applies to large and sparse nonlinear systems of equations, and uses the Q-R factorization of the approximate Jacobians. This method belongs to a more general class of algorithms for which we prove a local convergence theorem. Some numerical experiments seem to confirm that the new algorithm is reliable.
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  • 55
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    Computing 38 (1987), S. 185-207 
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    Description / Table of Contents: Zusammenfassung Wir diskutieren ein mathematisches Modell für die Filterung einer Flüssigkeit durch ein poröses Medium. Das Modell führt auf ein freies Randwertproblem, dessen Gleichung von der Retentionsfunktion abhängt. Mit Hilfe einer numerischen Finite-Elemente-Approximation werden ein Existenz- und Eindeutigkeitssatz sowie Fehlerabschätzungen für den Fall einer linearen Retentionsfunktion hergeleitet.
    Notes: Abstract We discuss a mathematical model arising in the filtration of a fluid through a porous medium. The model leads to a free boundary value problem whose governing equation depends on the retention function. A numerical approximation by means of finite elements is used to obtain an existence and uniqueness theorem along with an error estimate for a linear retention function.
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    Computing 38 (1987), S. 209-218 
    ISSN: 1436-5057
    Keywords: Guaranteed errorbounds for hyperbolic problems ; approximated operators ; errorestimation automatically
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    Description / Table of Contents: Zusammenfassung Es wird ein neu entwickeltes und implementiertes Verfahren zur Berechnung von garantierten Fehlerschranken bei hyperbolischen Anfangswert-problemen beschrieben. Die grundlegenden Konzepte—modifizierte Fixpunktsätze und angenäherte Operatoren—gestatten eine automatische a posteriori Fehlerabschätzung. Deshalb ist keine a priori Kenntnis von Lipschitzkonstanten, Monotonieeigenschaften oder zusätzliche Fehleranalyse erforderlich.
    Notes: Abstract This article describes a newly developed and implemented method for computing guaranteed errorbounds for the solution of hyperbolic initial value problems. The basic concepts—modified fixed point theorems and approximated operators—allow an a posteriori error-estimation automatically. Therefore, no a priori knowledge of Lipschitz constants, monotonicity properties or additional error analysis is necessary.
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    Computing 38 (1987), S. 261-267 
    ISSN: 1436-5057
    Keywords: 65D07 ; 41A15 ; Existence conditions ; construction os positive splines ; minimization of the curvature
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    Description / Table of Contents: Zusammenfassung Unter positiver Interpolation wird die Aufgabenstellung verstanden, zur einer nichtnegativen Datenmenge nichtnegative Interpolierende zu konstruieren. Im Fallen rational-quadratischer Splines wird eine notwendige und hinreichende Bedingung für die Durchführbarkeit positiver Interpolation hergeleitet, und es wird gezeigt, daß diese sich bei passender Wahl der vorkommenden Parameter stets erfüllen läßt.
    Notes: Abstract A necessary and sufficient criterion is presented under which the property of positivity carry over from the data set to rational quadratic spline interpolants. The criterion can always be satisfied if the occuring parameters are properly chosen.
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    Computing 38 (1987), S. 299-313 
    ISSN: 1436-5057
    Keywords: 65D05 ; 41A10 ; Interpolation ; local piecewise polynomials ; ratio slope
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    Description / Table of Contents: Zusammenfassung Ein Satz diskreter Datenwerte über dem Intervall [a, b], der eine Funktiong (x) repräsentiert, wird stückweise durch lokal definierte kubische Polynome interpoliert. Die entstehende Interpolationsfunktion hat folgende Eigenschaften: sie ist monoton und/oder konvex und repräsentiert alle durch die Daten vorgegebenen Wendepunkte, wobei keine zusätzlichen Wendepunkte erzeugt werden. Das Approximationsverfahren wird in Form eines FORTRAN 77-Unterprogramms angegeben.
    Notes: Abstract The interpolation of a discrete set of data, on the interval [a, b], representing the functiong(x) is obtained using a local piecewise polynomial of order 3. This piecewise cubic interpolant has the following properties: monotonicity and/or convexity or turning points that are present in the data are preserved and no extraneous turning points are created. This approximation method is also presented in the form of a FORTRAN77 subroutine.
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    Computing 38 (1987), S. 325-340 
    ISSN: 1436-5057
    Keywords: 90 C 08 ; 68 E 10 ; Linear assignment problem ; shortest path methods ; Pascal implementation
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    Description / Table of Contents: Zusammenfassung Wir entwickeln einen Algorithmus mit kürzesten alternierenden Wegen für das lineare Zuordnungsproblem. Er enthält neue Routinen für die Anfangswerte und eine spezielle Implementierung der Kürzesten-Wege-Methode von Dijkstra. Sowohl für dichte als auch für dünne Probleme zeigen Testläufe, daß unser Algorithmus gleichmäßig schneller als die besten Algorithmen aus der Literatur ist. Eine Implementierung in Pascal wird angegeben.
    Notes: Abstract We develop a shortest augmenting path algorithm for the linear assignment problem. It contains new initialization routines and a special implementation of Dijkstra's shortest path method. For both dense and sparse problems computational experiments show this algorithm to be uniformly faster than the best algorithms from the literature. A Pascal implementation is presented.
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    Description / Table of Contents: Zusammenfassung Es wird ein nichtlineares Differential-Differenzengleichungssystem mit Impulsen behandelt und eine Approximationsmethode zur Ermittlung periodischer Lösungen des betrachteten Systems angegeben.
    Notes: Abstract A non-linear system of differential-difference equations with impulses is considered. An approximate method for finding the periodic solution of the considered system is constructed and justified.
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    Computing 39 (1987), S. 1-17 
    ISSN: 1436-5057
    Keywords: Primary 65H ; Secondary 47H ; Hysteresis points ; cusp points ; turning points ; inexact Newton method ; local convergence
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    Description / Table of Contents: Zusammenfassung Es wird ein direktes, Verfahren zur Berechnung eines Hysteresepunktes (zweifacher Rückkehrpunkt), der in Beziehung zu einem Cusp-Punkt eines nichtlinearen, von zwei Parametern abhängenden Systems vonn Gleichungen inn Variablen steht, beschrieben. Ein minimal erweitertes, nichtlineares Gleichungssystem wird durch Anfügen von zwei Gleichungen konstruiert, das den Hysteresepunkt als isolierte Lösung besitzt. Es wird eine effektive Implementierung des Newton-Verfahrens vorgestellt, die ohne die Berechnung zweiter Ableitungen des Originalproblems arbeitet. Zwei Beispiele zeigen die Wirksamkeit desQ-quadratisch konvergenten Verfahrens.
    Notes: Abstract A direct method is described for computing a hysteresis point (double turning point) corresponding to a cusp point of a system ofn nonlinear equations inn variables depending on two parameters. By addition of two equations a minimally extended system ofn+2 nonlinear equations is constructed for which the hysteresis point is an isolated solution. An efficient implementation of Newton's method is presented not requiring evaluations of second derivatives of the original problem. Two numerical examples show the efficiency of theQ-quadratically convergent method.
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    Computing 39 (1987), S. 43-55 
    ISSN: 1436-5057
    Keywords: Primary 65 R 20 ; secondary 45 L 10 ; Tikhonov-regularization ; Hilbert scales ; discrepancy principle ; linear integral equations
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    Description / Table of Contents: Zusammenfassung Wir diskutieren die numerische Realisierung einer a-posteriori Parameterwahl für die Tikhonov Regularisierung von linearen Integralgleichungen erster Art in Hilbertskalen, die optimale Konvergenzraten liefert und die keine Information über die exakte Lösung benötigt. Numerische Beispiele bestätigen die theoretischen Ergebnisse.
    Notes: Abstract We discuss the numerical realization of an a-posteriori parameter choice for Tikhonov regularization of linear integral equations of the first kind in Hilbert scales that leads to optimal convergence rates and that does not need any information about the exact solution. Numerical examples confirm the theoretical results.
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    Computing 39 (1987), S. 345-351 
    ISSN: 1436-5057
    Keywords: Graph coloring ; tabu search ; simulated annealing
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    Description / Table of Contents: Zusammenfassung Tabu-Methoden werden benützt, um schrittweise den minimalen Wert einer Funktion zu erreichen. Eine sogenannte Tabuliste von verbotenen Schritten wird während des Prozesses nachgeführt, so daß man im Algorithmus keine Zyklen hat und nicht in lokalen Minima gefangen wird. Solche Methoden werden auf Graphenfärbung angepaßt. Wir zeigen, daß man mit dieser Technik fast optimale Färbungen für Graphen mit bis zu 1000 Knoten erhält. Die Effizienz dieser Methoden ist viel besser als diejenige der berühmten „Simulated Annealing” Algorithmen.
    Notes: Abstract Tabu search techniques are used for moving step by step towards the minimum value of a function. A tabu list of forbidden movements is updated during the iterations to avoid cycling and being trapped in local minima. Such techniques are adapted to graph coloring problems. We show that they provide almost optimal colorings of graphs having up to 1000 nodes and their efficiency is shown to be significantly superior to the famous simulated annealing.
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    Computing 39 (1987), S. 371-375 
    ISSN: 1436-5057
    Keywords: 65 G 10 ; Interval analysis ; matrix inversion
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    Description / Table of Contents: Zusammenfassung Für die intervallmäßigen Schulz-Verfahren zur Einschließung der Inversen einer Matrix wird eine notwendige und hinreichende Bedingung dafür angegeben, daß eine Ausgangseinschließung derart existiert, so daß die Iterierten in beiden Schranken streng monotone Folgen bilden. Ferner wird eine berechenbare Startintervallmatrix mit dieser Eigenschaft angegeben.
    Notes: Abstract In this note we are considering the interval versions of Schulz's method for bounding the inverse of a matrix. We prove a necessary and sufficient criterion for the existence of an interval inclusion such that the iterates are strictly monotonic in both bounds. In particular, such an initial interval-matrix is constructed.
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    Graphs and combinatorics 3 (1987), S. 95-109 
    ISSN: 1435-5914
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    Topics: Computer Science , Mathematics
    Notes: Abstract We prove the following result. LetΓ be a finite distance-regular graph. Letc i ,a i ,b i be the intersection numbers ofΓ. IfΓ is not an ordinaryn-gon, then the number of (c i ,a i ,b i ) such thatc i =b i is bounded by a certain function of the valencyk, say 10k2 k .
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    Graphs and combinatorics 3 (1987), S. 325-339 
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    Notes: Abstract We give the generating function for parallelogram polyominoes according to the bond perimeter and the site perimeter. In this last case, we give an asymptotic evaluation for their number. According to the two parameters an exact formula for their number is found which gives some numbers closed to the Narayana's numbers.
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    Graphs and combinatorics 3 (1987), S. 341-347 
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    Notes: Abstract Letf(n, k) denote the maximum length of a sequence (F 1,F 2,...) of distinct subsets of ann-element set with the property that|F i ∖F j | 〈 k for alli 〈 j. We determine the exact values off(n, 2) and characterize all the extremal sequences. Fork ≥ 3 we prove that $$f(n,k) = (1 + o(1))\left( {\begin{array}{*{20}c} n \\ k \\ \end{array} } \right)$$ . Some related problems are also considered.
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    Graphs and combinatorics 3 (1987), S. 349-356 
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    Notes: Abstract If a given graphG can be obtained bys vertex identifications from a suitable graph embeddable in the projective plane ands is the minimum number for which this is possible thens is called the splitting number ofG in the projective plane. Here a formula for the splitting number of the complete graph in the projective plane is derived.
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    Graphs and combinatorics 3 (1987), S. 365-377 
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    Notes: Abstract In this paper we construct pairwise balanced designs (PBDs) having block sizes which are prime powers congruent to 1 modulo 6. Such a PBD containsn = 6r + 1 points, for some positive integerr. We show that this condition is sufficient forn ≥ 1927, with at most 31 possible exceptions below this value. As an immediate corollary, we prove that there exists a pair of orthogonal Steiner triple systems of ordern, for the same values ofn.
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    Graphs and combinatorics 3 (1987), S. 1-6 
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    Notes: Abstract A connected graphG is said to beF-good if the Ramsey numberr(F, G) is equal to(x(F) − 1)(p(G) − 1) + s(F), wheres(F) is the minimum number of vertices in some color class under all vertex colorings by χ (F) colors. It is of interest to know which graphsF have the property that all trees areF-good. It is shown that any large tree isK(1, 1,m 1,m 2,...,m t )-good.
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    Graphs and combinatorics 3 (1987), S. 25-38 
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    Notes: Abstract One of the main results says that ifC is a binary linear code of length 4t and of dimension greater than 2t, thenC contains a word of weight 2t and this bound is best possible. Several results of similar flavor are established both for linear and non-linear codes. For the proof a lemma introducing the binormal forms of binary matrices is needed. The results are applied to determine the coset chromatic number of Hadamard graphs, to solve a problem of Galvin and to give a short proof of a theorem of Gleason on self-dual doubly-even codes.
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    Graphs and combinatorics 3 (1987), S. 45-53 
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    Notes: Abstract The reconstruction numberrn(G) of a graphG was introduced by Harary and Plantholt as the smallest number of vertex-deleted subgraphsG i =G − v i in the deck ofG which do not all appear in the deck of any other graph. For any graph theoretic propertyP, Harary defined theP-reconstruction number of a graph G ∈P as the smallest number of theG i in the deck ofG, which do not all appear in the deck of any other graph inP We now study the maximal planar graph reconstruction numberℳrn(G), proving that its value is either 1 or 2 and characterizing those with value 1.
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    Queueing systems 1 (1987), S. 265-277 
    ISSN: 1572-9443
    Keywords: Stochastic ordering ; random walks ; ladder epochs ; maximum and minimum ; bulk queues ; queue length ; busy period ; group arrivals ; batch service ; service capacity
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    Notes: Abstract We consider two important classes of single-server bulk queueing models: M(X)/G(Y)/1 with Poisson arrivals of customer groups, and G(X)/m(Y)1 with batch service times having exponential density. In each class we compare two systems and prove that one is more congested than the other if their basic random variables are stochastically ordered in an appropriate manner. However, it must be recognized that a system that appears congested to customers might be working efficiently from the system manager's point of view. We apply the results of this comparison to (i) the family {M/G(s)/1,s ⩾ 1} of systems with Poisson input of customers and batch service times with varying service capacity; (ii) the family {G(s)/1,s ⩾ 1} of systems with exponential customer service time density and group arrivals with varying group size; and (iii) the family {M/D/s,s⩾ 1} of systems with Poisson arrivals, constant service time and varying number of servers. Within each family, we find the system that is the best for customers, but this turns out to be the worst for the manager (or vice versa). We also establish upper (or lower) bounds for the expected queue length in steady state and the expected number of batches (or groups) served during a busy period. The approach of the paper is based on the stochastic comparison of random walks underlying the models.
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    Queueing systems 1 (1987), S. 289-309 
    ISSN: 1572-9443
    Keywords: Queueing theory ; synchronization ; assembly-like queues ; decomposition ; approximation
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    Notes: Abstract Assembly-like queues model assembly operations where separate input processes deliver different types of component (customer) and the service station assembles (serves) these input requests only when the correct mix of components (customers) is present at the input. In this work, we develop an effective approximate analytical solution for an assembly-like queueing system withN(N ⩾ 2) classes of customers formingN independent Poisson arrival streams with rates {λi=1,...,N} The arrival of a class of customers is “turned off” whenever the number of customers of that class in the system exceeds the number for any of the other classes by a certain amount. The approximation is based on the decomposition of the originalN input stream stage into a cascade ofN-1 two-input stream stages. This allows one to refer to the theory of paired customer systems as a foundation of the analysis, and makes the problem computationally tractable. Performance measures such as server utilization, throughput, average delays, etc., can then be easily computed. For illustrative purposes, the theory and techniques presented are applied to the approximate analysis of a system withN = 3. Numerical examples show that the approximation is very accurate over a wide range of parameters of interest.
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    Queueing systems 2 (1987), S. 307-320 
    ISSN: 1572-9443
    Keywords: Group arrivals ; exhaustive service discipline ; phase-type service times
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    Notes: Abstract Queues with compound Poisson arrivals, phase-type service and exhaustive service discipline are studied. An algorithmic method is developed to compute the steady-state probability distribution of the number of customers in the system with unlimited or limited queue capacities. Examples with different model parameters are given to show the computational efficiency of the method. In the Appendix, the stochastic decomposition property for the queues with single arrivals and with exhaustive service discipline is extended to queues with group arrivals.
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    Queueing systems 2 (1987), S. 333-349 
    ISSN: 1572-9443
    Keywords: queueing ; maintenance ; manufacturing ; reliability
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    Notes: Abstract This paper considers the maintenance of an unreliable M/G/1 queue-like job shop, integrating the maintenance process and the resulting queue operating characteristics. The system may breakdown, leading to unscheduled maintenance. Otherwise, preventive maintenance is done whenn jobs have been processed — whichever comes first. Using arguments from renewal theory, basic results regarding the queue-maintenance policy are established. Both an analytical and numerical example are studied in detail.
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    Queueing systems 2 (1987), S. 393-398 
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    Queueing systems 2 (1987), S. 399-399 
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    Queueing systems 2 (1987), S. 67-82 
    ISSN: 1572-9443
    Keywords: Nonproduct form networks ; batch and interactive jobs ; exact solutions ; FIFO ; LIFO
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    Notes: Abstract Networks of queues with finite and infinite source customers have been used to study the interaction between the batch jobs and interactive jobs in computer systems. Earlier Kaufman ([1], PP-345-348) developed accurate approximations for a simple nonproduct form network of this type. In this paper we offer exact solutions for the same model with one finite source customer. We study both FIFO and LIFO disciplines at the contention node. The results are derived for the case where the finite source think time and service time distributions are generalized hyperexponential.
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    Queueing systems 2 (1987), S. 173-185 
    ISSN: 1572-9443
    Keywords: Roots ; random group arrival ; single server ; probability distribution
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    Notes: Abstract This paper deals with numerical computations for the bulk-arrival queueing modelGI X/M/1. First an algorithm is developed to find the roots inside the unit circle of the characteristic equation for this model. These roots are then used to calculate both the moments and the steady-state distribution of the number of customers in the system at a pre-arrival epoch. These results are used to compute the distribution of the same random variable at post-departure and random epochs. Unifying the method used by Easton [7], we have extended its application to the special cases where the interarrival time distribution is deterministic or uniform, and to cases whereX has a given arbitrary distribution. We also improved on the various root-finding methods used by several previous authors so that high values of the parameters, in particular large batch sizes, can be investigated as well.
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    Queueing systems 2 (1987), S. 235-244 
    ISSN: 1572-9443
    Keywords: Queues with ordered entry ; sample path comparison ; point processes
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    Notes: Abstract We study a queueing system withm exponential servers with distinct service rates. Jobs arrive at the system following an arbitrary point process. Arrived jobs receive service at the first unoccupied server (if any) according to an entry order π, which is a permutation of the integers 1, 2,...,m. The system has a finite buffer capacity. When the buffer limit is reached, arrivals will be blocked. Blocked jobs will either be lost or come back as New arrivals after a random travel time. We are concerned with the dynamic stochastic behavior of the system under different entry orders. A partial ordering is established among entry orders, and is shown to result in some quite strong orderings among the associated stochastic processes that reflect the congestion and the service characteristics of the system. The results developed here complement existing comparison results for queues with homogeneous servers, and can be applied to aid the design of conveyor and communication systems.
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    Queueing systems 2 (1987), S. 285-305 
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    Keywords: State-dependent queues ; busy period analysis ; singular perturbations
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    Notes: Abstract We consider a state-dependent M/M/1 queue in which the arrival rate is a function of the instantaneous unfinished work (work backlog) in the system, and the customer's exponential service time distribution is allowed to depend on the unfinished work in the system at the instant that customer arrived. We obtain asymptotic approximations to both the busy period distributions as well as the residual busy period distribution. Our approximations are valid for systems with a rapid arrival rate and small mean service times.
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    Queueing systems 2 (1987), S. 351-361 
    ISSN: 1572-9443
    Keywords: GI/G/1 queue ; approximation ; waiting time distribution
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    Notes: Abstract The Sokolov procedure is described and used to obtain an explicit and easily applied approximation for the waiting time distribution in the FIFO GI/G/1 queue.
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    Queueing systems 2 (1987), S. 373-380 
    ISSN: 1572-9443
    Keywords: Correlation ; estimation ; waiting times ; GI/M/m queue
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    Notes: Abstract Serial correlation coefficients are useful measures of the interdependence of successive waiting times. Potential applications include the development of linear predictors and determining simulation run lengths. This paper presents the algorithm for calculating such correlations in the multiserver exponential service queue, and relates it to known results for single server queues.
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    Queueing systems 2 (1987), S. 387-392 
    ISSN: 1572-9443
    Keywords: Departure process ; filtering theory ; insensitivity ; M/M/1 queues ; point processes ; queueing theory ; tandem queues
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    Notes: Abstract Given a finite number of empty ./M/1 queues, let customers arrive according to an arbitrary arrival process and be served at each queue exactly once, in some fixed order. The process of departing customers from the network has the same law, whatever the order in which the queues are visited. This remarkable result, due to R. Weber [4], is given a simple probabilistic proof.
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    Queueing systems 1 (1987), S. 217-247 
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    Keywords: Statistical analysis of queueing systems ; estimation problems in queueing theory ; hypothesis testing in queueing theory ; inference in queueing theory
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    Notes: Abstract This paper provides an overview of the literature on statistical analysis of queueing systems. Topics discussed include: model identification, estimation, hypothesis testing and other related aspects. Not all of these statistical problems are covered in books on queueing theory or stochastic processes. The bibliography is not exhaustive, but comprehensive enough to provide sources from the literature.
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    Queueing systems 1 (1987), S. 279-287 
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    Keywords: Queueing theory ; conservation laws ; Little's Law ; limit theorems ; central limit theorem ; law of the iterated logarithm ; invariance principle ; regenerative processes
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    Notes: Abstract The familiar queueing principle expressed by the formulaL=λW can be interpreted as a relation among strong laws of large numbers. In a previous paper, we showed that this principle can be extended to include relations among other classical limit theorems such as central limit theorems and laws of the iterated logarithm. Here we provide sufficient conditions for these limit theorems using regenerative structure.
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    Queueing systems 1 (1987), S. 317-333 
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    Keywords: Queueing theory ; Bayesian analysis of queues ; Shannon information ; subjective probability ; discrete DFR distributions
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    Topics: Computer Science
    Notes: Abstract This is the first of an expository two-part paper which outlines a point of view different from that currently used in queueing theory. In both parts, the focus is on concepts. Here we adopt a personal probability point of view to all sources of uncertainty in the theory of queues and explore the consequences of our approach by comparing our results to those that are currently available. For ease of exposition, we confine attention to the M/M/1/∞ and the M/M/1/K queues. In Part I we outline the general strategy and focus on model development. In Part II we address the problem of inference in queues within the subjective Bayesian paradigm and introduce a use of Shannon's measure of information for assessing the amount of information conveyed by the various types of data from queues.
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  • 89
    ISSN: 1572-9443
    Keywords: Bayesian analysis ; Shannon information ; subjective probability ; discrete DFR distributions ; mixtures of exponentials
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    Topics: Computer Science
    Notes: Abstract This is a sequel to Part I of “A Subjective Bayesian Approach to the Theory of Queues”. The focus here is on inference and a use of Shannon's measure of information for assessing the amount of information conveyed by the various types of data from queues. The notation and terminology used here is established in Part I.
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  • 90
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    Queueing systems 2 (1987), S. 1-17 
    ISSN: 1572-9443
    Keywords: Processor-sharing models ; sojourn time distributions ; queue-length ; response time ; time sharing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper reviews some recent results based on new techniques used in the analysis of main processor-sharing queueing systems. These results include the solutions of the problems of determining the sojourn time distributions and the distributions of the number of jobs in the M/G/1/t8 queue under egalitarian and feedback (foreground-background) processor-sharing disciplines. A brief discussion of some related results is also given.
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  • 91
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    Queueing systems 2 (1987), S. 41-65 
    ISSN: 1572-9443
    Keywords: Transient behavior ; approach to steady state ; relaxation times ; birth- and-death process ; queues ; Brownian motion ; first passage times ; busy period ; complete monotonicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper presents some new perspectives on the time-dependent behavior of the M/M/1 queue. The factorial moments of the queue length as functions of time when the queue starts empty have interesting structure, which facilitates developing approximations. Simple exponential and hyperexponential approximations for the first two moment functions help show how the queue approaches steady state as time evolves. These formulas also help determine if steady-state descriptions are reasonable when the arrival and service rates are nearly constant over some interval but the process does not start in steady state.
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  • 92
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    Queueing systems 2 (1987), S. 147-172 
    ISSN: 1572-9443
    Keywords: Markov chains ; reduced systems ; steady-state probabilities ; queueing theory ; first passage times
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract A reduced system is a smaller system derived in the process of analyzing a larger system. While solving for steady-state probabilities of a Markov chain, generally the solution can be found by first solving a reduced system of equations which is obtained by appropriately partitioning the transition probability matrix. In this paper, we catagorize reduced systems as standard and nonstandard and explore the existence of reduced systems and their properties relative to the original system. We also discuss first passage probabilities and means for the standard reduced system relative to the original system. These properties are illustrated while determining the steady-state probabilities and first passage time characteristics of a queueing system.
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  • 93
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    Queueing systems 2 (1987), S. 187-200 
    ISSN: 1572-9443
    Keywords: GI/M/∞ ; batch arrivals ; batch arrival- and time-stationary probabilities ; binomial moments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this note, the GI/M/∞ queue with batch arrivals of constant sizek is investigated. It is shown that the stationary probabilities that an arriving batch findsi customers in the system can be computed in terms of the corresponding binomial moments (Jordan's formula), which are determined by a recursive relation. This generalizes well-known results by Takács [12] for GI/M/∞. Furthermore, relations between batch arrival- and time-stationary probabilities are given.
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  • 94
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    Queueing systems 2 (1987), S. 245-259 
    ISSN: 1572-9443
    Keywords: Two-dimensional Markov processes ; finite state space ; breakdowns ; server availability ; partial differential equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Two models involving multiprocessor systems with two different groups of processors are examined. In the first model, the processors which are in use break down from time to time; one of the two groups is used only when the other one is entirely inoperative. In the second model, the breakdowns are replaced by a Poisson stream of jobs. Again, one group of processors is used in preference to the other one. In both cases, the analysis is based on finding a polynomial in two variables which satisfies a partial differential-functional equation. Exact solutions are obtained.
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  • 95
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    Queueing systems 2 (1987), S. 381-386 
    ISSN: 1572-9443
    Keywords: Bulk service ; transient solution ; busy period ; virtual waiting time ; regenerative process ; server vacations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this paper we consider a single server queueing system with Poisson input, general service and a waiting room that allows only a maximum of ‘b’ customers to wait at any time. A minimum of ‘a’ customers are required to start a service and the server goes for a vacation whenever he finds less than ‘a’ customers in the waiting room after a service. If the server returns from a vacation to find less than ‘a’ customers waiting, he begins another vacation immediately. Using the theory of regenerative processes we derive expressions for the time dependent system size probabilities at arbitrary epochs.
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  • 96
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    Queueing systems 1 (1987), S. 375-399 
    ISSN: 1572-9443
    Keywords: State dependent M/G/1 queue ; Markov modulated queues ; busy period ; singular perturbations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We consider an M/G/1 queue where the arrival and service processes are modulated by a two state Markov chain. We assume that the arrival rate, service time density and the rates at which the Markov chain switches its state, are functions of the total unfinished work (buffer content) in the queue. We compute asymptotic approximations to performance measures such as the mean residual busy period, mean length of a busy period, and the mean time to reach capacity.
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  • 97
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    Queueing systems 2 (1987), S. 19-39 
    ISSN: 1572-9443
    Keywords: Queues ; bulk service ; statistical group testing ; Markov chains ; algorithmic probability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We consider a queueing model in which items wait to undergo group testing in batches of sizem. However, if fewer thanm items are present at the beginning of a service, items are tested singly. Ifm or more items are waiting at such an epoch, a group of sizem is tested and, if the group passes the test, allm items leave the system. When a group is found to contain at least one defective item, them items in it are retested individually. An algorithm is developed to compute many steady-state probabilities related to this queue. Comparisons of these probabilities are used to assess the effect of the group sizem on the behavior of the queue of items waiting for testing.
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  • 98
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    Queueing systems 2 (1987), S. 83-92 
    ISSN: 1572-9443
    Keywords: Telecommunications networks ; queues ; optimal design ; equitable charges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We study a multi-administration telecommunications network that is an abstraction of an international network. The nodes represent separate telecommunications administrations that are linked such that alternately-routed calls go through one tandem administration. The cost of the group of circuits between a pair of administrations is borne by them; and when a call between the pair is alternately routed through the tandem node, then the two administrations share the call revenue and pay transit fees to the tandem administration. The numbers of circuits between the administrations are selected to yield a least-cost network that provides a desired level of service, in terms of blocking probabilities, over an entire day. We address the problem of determining transit charges for the alternately-routed calls that are equitable for all of the administrations. Our approach is to derive such charges by equating the system-optimal circuit group sizes to certain hypothetical administration-optimal circuit group sizes. This approach may be of use in other system design problems involving cost sharing among several companies.
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  • 99
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    Queueing systems 2 (1987), S. 115-145 
    ISSN: 1572-9443
    Keywords: Polling systems ; disk systems ; disk SCAN policy ; shortest-seek-time-first disk scheduling ; moving-server systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract A single server moves with speed υ on a line interval (or a circle) of length (circumference)L. Customers, requiring service of constant durationb, arrive on the interval (or circle) at random at mean rate λ customers per unit length per unit time. A customer's mean wait for service depends partly on the rules governing the server's motion. We compare two different servers: thepolling server and thegreedy server. Without knowing the locations of waiting customers, a polling server scans endlessly back and forth across the interval (or clockwise around the circle), stopping only where it encounters a waiting customer. Knowing where customers are waiting, a greedy server always travels toward the current nearest one. Except for certain extreme values of υ,L, b, andλ, the polling and greedy servers are roughly equally effective. Indeed, the simpler polling server is often the better. Theoretical results show, in most cases, that the polling server has a high probability of moving toward the nearest customer, i.e. moving as a greedy server would. The greedy server is difficult to analyze, but was simulated on a computer.
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  • 100
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    Queueing systems 2 (1987), S. 201-233 
    ISSN: 1572-9443
    Keywords: Imbedded Markov chain ; retrial queues ; stochastic decomposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Queueing systems in which arriving customers who find all servers and waiting positions (if any) occupied may retry for service after a period of time are called retrial queues or queues with repeated orders. Retrial queues have been widely used to model many problems in telephone switching systems, telecommunication networks, computer networks and computer systems. In this paper, we discuss some important retrial queueing models and present their major analytic results and the techniques used. Our concentration is mainly on single-server queueing models. Multi-server queueing models are briefly discussed, and interested readers are referred to the original papers for details. We also discuss the stochastic decomposition property which commonly holds in retrial queues and the relationship between the retrial queue and the queue with server vacations.
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