@misc{Deuflhard1990, author = {Deuflhard, Peter}, title = {Global Inexact Newton Methods for Very Large Scale Nonlinear Problems.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-303}, number = {SC-90-02}, year = {1990}, abstract = {Newton methods for nonlinear problems are known to require the solution of a sequence of linear problems of the same type. For very large scale problems, as understood herein, the arising linear systems can only be solved by iterative methods. Then Newtons iteration appears as outer iteration. The question of interest will be to control the accuracy of the inner iteration such that the convergence speed of Newtons method is preserved. The purpose of the paper is to combine the concept of inexact Newton methods with the concept of the affine invariant exact Newton methods - which is important for problems with ill- conditioned Jacobian matrices (such as typical 2-D or 3-D discretized partial differential equations).}, language = {en} } @misc{WulkowDeuflhard1990, author = {Wulkow, Michael and Deuflhard, Peter}, title = {Towards an Efficient Computational Treatment of Heterogeneous Polymer Reactions.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-292}, number = {SC-90-01}, year = {1990}, abstract = {The discrete Galerkin method developed by the authors has turned out to be an efficient tool for the computational treatment of very large scale ODE systems arising in polyreaction kinetics. Up to now, this approach has been worked out in detail for homogeneous polymer reactions. The present paper deals with one line of possible extensions of the method to the case of so-called heterogeneous processes, which may appear e. g. in smog reactions. The associated mathematical models involve reaction coefficients depending on the chain length of the reacting polymer. The herein suggested extension is worked out in some detail on the basis of the earlier paper. In addition, a numerical example describing polymer degradation is included.}, language = {en} } @misc{Hoppe1989, author = {Hoppe, Ronald H. W.}, title = {Numerical Solution of Multicomponent Alloy Solidification by Multi-Grid Techniques.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-285}, number = {SC-89-10}, year = {1989}, abstract = {The solidification of an \$ N \$-component alloy is described by an initial boundary value problem for a system of degenerate parabolic equations modelling heat conduction and mass diffusion. Discretizing implicitly in time and by piecewise linear finite elements in the space variables, at each time step the solution of a system of quasivariational inequalities is required. For the numerical solution of that system, a multi-grid algorithm is developed by making use of game theoretic concepts and duality arguments from convex analysis. Finally, the efficiency of the algorithm is demonstrated by displaying numerical results for a ternary alloy.}, language = {en} } @misc{Yserentant1989, author = {Yserentant, Harry}, title = {Two Preconditioners Based on the Multi-Level Splitting of Finite Element Spaces.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-274}, number = {SC-89-09}, year = {1989}, abstract = {The hierarchical basis preconditioner and the recent preconditioner of BRAMBLE, PASCIAK and XU are derived and analyzed within a joint framework. This discussion elucidates the close relationship between both methods. Special care is devoted to highly nonuniform meshes; our theory is based exclusively on local properties like the shape regularity of the finite elements.}, language = {en} } @misc{Maierhoefer1989, author = {Maierh{\"o}fer, Gerhard}, title = {Ein paralleler adaptiver Algorithmus f{\"u}r die numerische Integration.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-265}, number = {SC-89-08}, year = {1989}, abstract = {Der Bericht ist die Ausarbeitung eines Vortrages, der auf dem Transputer Anwender Treffen (TAT'89) im September 1989 gehalten wurde. Es wird die Parallelisierung und Implementierung eines adaptiven Algorithmus zur numerischen Integration (Romberg Quadratur) beschrieben. Ausgew{\"a}hlte Meßergebnisse sind enthalten. {\bf Keywords:} Numerischer Algorithmus, Romberg Quadratur, paralleler adaptiver Algorithmus, dynamische Lastverteilung und Prozessorzahl, lokaler Speicher, Nearest-Neighbour-Architektur, Transputer, TDS, OCCAM2.}, language = {de} } @misc{BuddeWulkow1989, author = {Budde, Uwe and Wulkow, Michael}, title = {Computation of Molecular Weight Distributions for Free Radical Polymerization Systems.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-253}, number = {SC-89-07}, year = {1989}, abstract = {Modeling of free radical polymerization leads to very large and usually stiff systems of ordinary differential equations which cannot be solved directly in an efficient way. This paper presents the application of a new approach called discrete Galerkin method to a realistic example - the polymerization of methyl methacrylate(MMA). The method is characterized by a Galerkin approximation on the basis of orthogonal polynomials of a discrete variable which represents the polymer degree. It allows the efficient computation of solutions of complete kinetic schemes with time- or moment-dependent reaction coefficients by reducing the complexity to a few differential equations. The approximation error can be controlled by an error estimation. In the case of MMA polymerization a reduction of computational effort by a factor of about 25 compared to a standard method can be obtained for the quasi-steady-state approximation of the model. In addition solutions of the instationary kinetic scheme can be easily computed.}, language = {en} } @misc{HuamoShuli1989, author = {Huamo, Wu and Shuli, Yang}, title = {MmB-A New Class of Accurate High Resolution Schemes for Conservation Laws in Two Dimensions.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-248}, number = {SC-89-06}, year = {1989}, abstract = {In this paper we present the MmB schemes, which preserve the local maximum and minimum bounds of the initial data in the smallest union of mesh elements of previous time step containing the domain of dependence of the solution on the mesh element with center at point \$ P \$\ under consideration. In 1-D, the MmB schemes are almost identical with TVD schemes. As well-known, there is no second-order TVD scheme in 2-D, nevertheless, we present here two classes of 2-D second-order accurate MmB-schemes. It is proved that 1-D discrete MmB (or TVD) and 1-D semi-discrete TVD schemes may have second-order accuracy at (nonsonic) critical points, but cannot be of uniformly second-order accurate in the whole neighborhood of the critical points. New accurate high resolution flux limiters are suggested. Numerical results for 1-D and 2-D test problems are given. {\bf Keywords:} Difference scheme, TVD, MmB, flux limiter.}, language = {en} } @misc{KornhuberRoitzsch1989, author = {Kornhuber, Ralf and Roitzsch, Rainer}, title = {On Adaptive Grid Refinement in the Presence of Internal or Boundary Layers.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-230}, number = {SC-89-05}, year = {1989}, abstract = {We propose an anisotropic refinement strategy which is specially designed for the efficient numerical resolution of internal and boundary layers. This strategy is based on the directed refinement of single triangles together with adaptive multilevel grid orientation. It is demonstrated by several numerical examples that compared to usual methods, the new anisotropic refinement ends up in more stable and more accurate solutions at much less computational cost. {\bf Keywords:} Adaptive finite elements, directed refinement, adaptive grid orientation, convection diffusion equation, internal and boundary layers.}, language = {en} } @misc{Moeller1989, author = {M{\"o}ller, H. Michael}, title = {Multivariate Rational Interpolation: Reconstruction of Rational Functions.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-227}, number = {SC-89-04}, year = {1989}, abstract = {In this paper we consider the problem of reconstructing a multivariate rational function, when only its values at sufficiently many points are known. We use for the reconstruction of bivariate rational functions a bivariate rational interpolation operator investigated by Siemaszko [7] and a new one, compare both by examples in a Computer Algebra system, and present their multivariate generalizations. {\bf Keywords:} Multivariate rational interpolation, reconstruction, symbolic computation.}, language = {en} } @misc{Huamo1989, author = {Huamo, Wu}, title = {On the Possible Accuracy of TVD Schemes.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-212}, number = {SC-89-03}, year = {1989}, abstract = {The paper presents a detailed analysis of the possible accuracy available for TVD schemes in one dimension with emphasis to the semi-discrete 1-D TVD schemes. The analysis shows that the widely accepted statement [1] of degeneration of accuracy at critical points for TVD schemes should be corrected. We have theorem: TVD schemes using flux limiters \$ \varphi \$ of the form [1], [2] may be second-order accurate at critical points if \$ \varphi \$ (3) + \$ \varphi \$(-1) = 2, but cannot be uniformly second-order accurate in the whole neighborhood of critical point. If \$ \varphi \$(1) = 1, then the TVD schemes are second-order accurate in the region of smooth solutions sufficiently far from the critical points. Two ways are suggested to improve the accuracy. Numerical example is given. {\bf Keywords:} Semi-discrete schemes, TVD, flux limiter, degeneration of accuracy.}, language = {en} } @misc{Zha1989, author = {Zha, Hongyuan}, title = {Restricted Singular Value Decomposition of Matrix Triplets.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-205}, number = {SC-89-02}, year = {1989}, abstract = {In this paper we introduce the concept of restricted singular values (RSV's) of matrix triplets. A theorem concerning the RSV's of a general matrix triplet \$ (A,B,C) \$, where \$ A \in C^{m\times n} \$, \$B\in C^{m\times p} \$ and \$ C\in C^{q\times n} \$, which is called restricted singular value decomposition (RSVD) of matrix triplets, is derived. This result generalizes the wellknown SVD, GSVD and the recently proposed product induced SVD (PSVD). Connection of RSV's with the problem of determination of matrix rank under restricted perturbation is also discussed. {\bf Keywords:} Matrix rank, singular values, generalized singular values, product induced singular values, restricted singular values, matrix decompositions.}, language = {en} } @misc{Zha1989, author = {Zha, Hongyuan}, title = {A Numerical Algorithm for Computing the Restricted Singular Value Decomposition of Matrix Triplets.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-194}, number = {SC-89-01}, year = {1989}, abstract = {This paper presents a numerical algorithm for computing the restricted singular value decomposition of matrix triplets (RSVD). It is shown that one can use unitary transformations to separate the regular part from a general matrix triplet. After preprocessing on the regular part, one obtains a matrix triplet consisting of three upper triangular matrices of the same dimensions. The RSVD of this special matrix triplet is computed using the implicit Kogbetliantz technique. The algorithm is well suited for parallel computation. {\bf Keywords:} Restricted singular values, matrix triplets, unitary transformations, implicit Kogbetliantz technique.}, language = {en} } @misc{ChowDengFiedler1989, author = {Chow, Shui-Nee and Deng, Bo and Fiedler, Bernold}, title = {Homoclinic Bifurcation at Resonant Eigen-values.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-181}, number = {SC-88-10}, year = {1989}, language = {en} } @misc{KornhuberRoitzsch1989, author = {Kornhuber, Ralf and Roitzsch, Rainer}, title = {Adaptive Finite-Elemet- Methoden f{\"u}r konvektionsdominierte Randwertprobleme bei partiellen Differentialgleichungen.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-170}, number = {SC-88-09}, year = {1989}, abstract = {Ausgangspunkt bei der Behandlung konvektiv dominierter, elliptischer Probleme sind die bekannten hierarchischen Finite-Element-Methoden f{\"u}r den rein elliptischen Fall. Als stabile Erweiterung des Standard-Galerkin-Verfahrens wird das Stromlinien-Diffusions-Verfahren durch physikalische {\"U}berlegungen motiviert und kurz diskutiert. Anschließend zeigen wir, daß diese Methode erst in Verbindung mit einer hier erstmals vorgestellten lokalen Ausrichtung der Kanten wirksam eingesetzt werden kann. Zusammen mit einer ebenfalls neu entwickelten richtungsorientierten Verfeinerungsstrategie erh{\"a}lt man eine erheblich stabilere, genauere und schnellere Aufl{\"o}sung von Grenzschichten als mit herk{\"o}mmlichen Methoden.}, language = {de} } @misc{HoppeKornhuber1988, author = {Hoppe, Ronald H. W. and Kornhuber, Ralf}, title = {Multi-Grid Solution of Two Coupled Stefan Equations Arising in Induction Heating of Large Steel Slabs.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-160}, number = {SC-88-08}, year = {1988}, abstract = {Induction heating of large steel slabs can be described by a coupled system of nonlinear evolution equations of Stefan type representing the temporal and spatial distribution of the induced magnetic field and the generated temperature within the slab. Discretizing these equations implicitly in time and by finite differences in space, at each time step the solution of a system of difference inclusions is required. For the solution of that system two multi-grid algorithms are given which combined with a nested iteration type continuation strategy to proceed in time result in computationally highly efficient schemes for the numerical simulation of the induction heating process. {\bf Keywords:} induction heating, system of two coupled Stefan equations, multi-grid algorithms. {\bf Subject Classification:} AMS(MOS): 35K60, 35R35, 65H10, 65N05, 65N20, 78A25, 78A55.}, language = {en} } @misc{MelenkMoellerNeun1988, author = {Melenk, Herbert and M{\"o}ller, H. Michael and Neun, Winfried}, title = {Symbolic Solution of Large Stationary Chemical Kinetics Problems.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-157}, number = {SC-88-07}, year = {1988}, abstract = {The paper presents a new application of computer algebra to the treatment of steady states of reaction systems. The method is based on the Buchberger algorithm. This algorithm was modified such that it can exploit the special structure of the equations derived from reaction systems, so even large systems can be handled. In contrast to numerical approximation techniques, the algebraic solution gives a complete and definite overview of the solution space and it is even applicable when parameter values are unknown or undetermined. The algorithm, its adaptation to the problem class and its application to selected examples are presented.}, language = {en} } @misc{DeuflhardWulkow1988, author = {Deuflhard, Peter and Wulkow, Michael}, title = {Computational Treatment of Polyreaction Kinetics by Orthogonal Polynomials of a Discrete Variable.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-140}, number = {SC-88-06}, year = {1988}, abstract = {The paper presents a new approach to the computational treatment of polyreaction kinetics. This approach is characterized by a Galerkin method based on orthogonal polynomials of a discrete variable, the polymer degree (or chain length). In comparison with the known competing approaches (statistical moment treatment, Galerkin methods for continuous polymer models), the suggested method is shown to avoid the disadvantages and preserve the adventages of either of them. The basic idea of the method is the construction of a discrete inner product associated with a reasonably chosen probability density function. For the so-called Schulz-Flory distribution one thus obtains the discrete Laguerre polynomials, whereas the Poisson distribution leads to the Charlier polynomials. Numerical experiments for selected polyreaction mechanisms illustrate the efficiency of the proposed method.}, language = {en} } @misc{DeuflhardLeinenYserentant1988, author = {Deuflhard, Peter and Leinen, P. and Yserentant, Harry}, title = {Concepts of an Adaptive Hierarchical Finite Element Code.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-131}, number = {SC-88-05}, year = {1988}, abstract = {The paper presents the mathematical concepts underlying the new adaptive finite element code KASKADE, which, in its present form, applies to linear scalar second-order 2-D elliptic problems on general domains. Starting point for the new development is the recent work on hierarchical finite element bases due to Yserentant (1986). It is shown that this approach permits a flexible balance between iterative solver, local error estimator, and local mesh refinement device - which are the main components of an adaptive PDE code. Without use of standard multigrid techniques, the same kind of computational complexity is achieved - independent of any uniformity restrictions on the applied meshes. In addition, the method is extremely simple and all computations are purely local - making the method particularly attractive in view of parallel computing. The algorithmic approach is illustrated by a well-known critical test problem. {\bf Keywords:} finite elements, hierarchical basis, adaptive mesh refinement, preconditioned conjugate gradient methods.}, language = {en} } @misc{MelenkNeun1988, author = {Melenk, Herbert and Neun, Winfried}, title = {Parallel Polynomial Operations in the Buchberger Algorithm.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-125}, number = {SC-88-04}, year = {1988}, abstract = {The Buchberger algorithm is a basic tool for the solution of systems of polynomial equations in an environment of computer algebra applications. A model for overlapped processing of different steps of the algorithm is presented, which uses the data structure of the polynomials (distributive representation) for synchronization. The model can be applied for multi processors with fast access to shared data. It is tested with Cray X-MP multi processors based on a parallel version of Portable Standard Lisp (PSL 3.4).}, language = {en} } @misc{AlexanderFiedler1988, author = {Alexander, J. C. and Fiedler, Bernold}, title = {Global Decoupling of Coupled Symmetric Oscillators.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-113}, number = {SC-88-03}, year = {1988}, abstract = {We model a symmetric system of coupled oscillators as a graph with symmetry group \$\gamma\$. Each vertex of the graph represents an "oscillator" or a "cell" of reactants. The magnitude (concentration) of the reactants in the \$ i \$ th cell is represented by a vector \$ x^i \$. The edges represent the coupling of the cells. The cells are assumed to evolve by identical reaction-diffusion equation which depends on the sum of the reactants in the nearest neighbors. Thus the dynamics of the system is described by a nonlinear differential system \begin{flushleft} \[ \mbox {(*) \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ } \dot{x}^i = f (x^i,\sum_{j \in N_i} x^j), \mbox { \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ } \] \end{flushleft} where the sum ranges over the set \$ N_i \$ of neighbors of cell \$ i \$ . If \$ f \$ also has a symmetry (e.g., oddness), there are geometric conditions on the graph such that the nonlinear system \$ (*) \$ decouples globally into a product flow on certain sums of isotropy subspaces. Thus we may detect higher-dimensional tori of solutions of \$ (*) \$ which are not amenable to other types of analysis. We present a number of examples, such as bipartite graphs, complete graphs, the square, the octahedron, and a 6-dimensional cube.}, language = {en} } @misc{MelenkMoellerNeun1988, author = {Melenk, Herbert and M{\"o}ller, H. Michael and Neun, Winfried}, title = {On Gr{\"o}bner Bases Computation on a Supercomputer Using REDUCE.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-107}, number = {SC-88-02}, year = {1988}, abstract = {Gr{\"o}bner bases are the main tool for solving systems of algebraic equations and some other problems in connection with polynomial ideals using Computer Algebra Systems. The procedure for the computation of Gr{\"o}bner bases in REDUCE 3.3 has been modified in order to solve more complicated algebraic systems of equations by some general improvements and by some tools based on the specific resources of the CRAY X-MP. We present this modification and illustrate it by examples.}, language = {en} }