Institut für Mathematik
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- Institut für Mathematik (2150) (remove)
Kurzautobiographie
(1995)
Geometrie im Raum, Folge 3
(1995)
General Relativity and Gravitation is a journal of studies in general relativity and related topics, published under the auspices of the International Committee on General Relativity and Gravitation. The journal publishes original, high-quality research papers on the theoretical and experimental aspects of general relativity and related topics; surveys and review articles on current research in general relativity and gravitation; news regarding conferences and other enterprises of interest to scientists in this field; and book reviews. All manuscripts and editorial correspondence, as well as books for review, should be submitted to the Editor, and authors may propose who among the Associate Editors will deal with their paper. All submitted articles are acknowledged and refereed.
Stoffdynamik in Geosystemen
(1995)
Die Reihe 'Stoffdynamik in Geosystemen' hat ihre Wurzeln in der interdisziplinären Projektarbeit der gleichnamigen Arbeitsgruppe. Im ersten Band'Wenn Abwasser die Landschaft verändert...' wurden am Beispiel der Abwasserbodenbehandlung die Probleme diskutiert und dokumentiert, welche aus der Überprägung von Naturräumen durch die Tätigkeit des Menschen resultieren. Im Band 2 'Neue Cocktails nur mit bewährten Rezepten?' wurde über die Weiter-entwicklung der theoretischen und methodischen Ansätze berichtet. Mathematische bzw. geophysikalische Methoden zur Aufklärung von Dynamik bzw. Struktur der Geosysteme bildeten den Gegenstand der 1999 und 2000 erschienen beiden Bände 'Nichtlineare Methoden zur Datenanalyse' bzw. 'Geophysik für Landwirtschaft und Bodenkunde'
Boundary value problems in Boutet de Monvel's algebra for manifolds with conical singularities II
(1995)
Hyperassociative semigroups
(1994)
Pre-solid varieties
(1994)
Many methods have been proposed for the stabilization of higher index differential-algebraic equations (DAEs). Such methods often involve constraint differentiation and problem stabilization, thus obtaining a stabilized index reduction. A popular method is Baumgarte stabilization, but the choice of parameters to make it robust is unclear in practice. Here we explain why the Baumgarte method may run into trouble. We then show how to improve it. We further develop a unifying theory for stabilization methods which includes many of the various techniques proposed in the literature. Our approach is to (i) consider stabilization of ODEs with invariants, (ii) discretize the stabilizing term in a simple way, generally different from the ODE discretization, and (iii) use orthogonal projections whenever possible. The best methods thus obtained are related to methods of coordinate projection. We discuss them and make concrete algorithmic suggestions.
A Hamiltonian system in potential form (formula in the original abstract) subject to smooth constraints on q can be viewed as a Hamiltonian system on a manifold, but numerical computations must be performed in Rn. In this paper methods which reduce "Hamiltonian differential algebraic equations" to ODEs in Euclidean space are examined. The authors study the construction of canonical parameterizations or local charts as well as methods based on the construction of ODE systems in the space in which the constraint manifold is embedded which preserve the constraint manifold as an invariant manifold. In each case, a Hamiltonian system of ordinary differential equations is produced. The stability of the constraint invariants and the behavior of the original Hamiltonian along solutions are investigated both numerically and analytically.
Many methods have been proposed for the simulation of constrained mechanical systems. The most obvious of these have mild instabilities and drift problems. Consequently, stabilization techniques have been proposed A popular stabilization method is Baumgarte's technique, but the choice of parameters to make it robust has been unclear in practice. Some of the simulation methods that have been proposed and used in computations are reviewed here, from a stability point of view. This involves concepts of differential-algebraic equation (DAE) and ordinary differential equation (ODE) invariants. An explanation of the difficulties that may be encountered using Baumgarte's method is given, and a discussion of why a further quest for better parameter values for this method will always remain frustrating is presented. It is then shown how Baumgarte's method can be improved. An efficient stabilization technique is proposed, which may employ explicit ODE solvers in case of nonstiff or highly oscillatory problems and which relates to coordinate projection methods. Examples of a two-link planar robotic arm and a squeezing mechanism illustrate the effectiveness of this new stabilization method.
In this paper, we show that symplectic partitioned Runge-Kutta methods conserve momentum maps corresponding to linear symmetry groups acting on the phase space of Hamiltonian differential equations by extended point transformation. We also generalize this result to constrained systems and show how this conservation property relates to the symplectic integration of Lie-Poisson systems on certain submanifolds of the general matrix group GL(n).