@misc{DeuflhardNowak, author = {Deuflhard, Peter and Nowak, Ulrich}, title = {Efficient Numerical Simulation and Identification of Large Chemical Reaction Systems.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-14}, number = {SC-86-01}, abstract = {New, highly efficient techniques for the numerical simulation and parameter identification of large chemical reaction systems are surveyed. The survey particularly addresses to chemists, which are understood to be potential users of the distributed software packages. These packages are written in the form of interactive dialogue systems - thus enabling chemists to concentrate on the chemistry of their problem. Large scale examples from chemical research environments are included.}, language = {en} } @misc{DeuflhardNowakWulkow, author = {Deuflhard, Peter and Nowak, Ulrich and Wulkow, Michael}, title = {Recent Developments in Chemical Computing.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-359}, number = {SC-90-07}, abstract = {The paper surveys three aspects of chemical computing, which seem to play a role in recent developments. First, extrapolation methods for the numerical treatment of differential- algebraic equations are introduced. The associated extrapolation code LIMEX has reached a certain level of sophistication, which makes it a real competitor to the elsewhere widely used multi-step code DASSL of Petzold. Second, adaptive methods of lines for partial differential equations such as those arising in combustion problems are treated. Both static and dynamic regridding techniques are discussed in some detail. Finally, some new ideas about the treatment of the kinetic equations arising from polymer reactions are presented. The new feature of the suggested approach is the application of a Galerkin procedure using sets of orthogonal polynomials over a discrete variable (which, of course, in the case of polymer reactions is the polymer degree). The new approach may open the door to a new reliable low dimensional treatment of complex polymer reactions.}, language = {en} } @misc{DeuflhardNowakPoehleetal., author = {Deuflhard, Peter and Nowak, Ulrich and P{\"o}hle, Uwe and Schmidt, B. Ch. and Weyer, J.}, title = {Die Ausbreitung von HIV/AIDS in Ballungsgebieten.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-4844}, number = {TR-91-09}, abstract = {The rapidly increasing number of AIDS cases requires a realistic estimation of the future development of the HIV/AIDS disease. For that purpose we develop a large system of coupled nonlinear differential equations describing simultaneously the dynamics of the development of the disease, the population size, the gender and age structure. A set of 1650 coupled equations are linked by balanced parameters. The balancing procedure is described by a set of (formally) 2,178,000 additional algebraic conditions. As the considered system is stiff, it requires new special extrapolation methods combined with techniquees of dynamical sparsing for the solution of sparsely filled systems. According to our simulations we expect 19,0,000 deaths caused by AIDS in the Federal Republic of Germany (former territories) in the year 2000. Such an epidemical spread would tie up about 4-7 percent of the actual health care workers.}, language = {de} } @misc{DeuflhardNowakWeyer, author = {Deuflhard, Peter and Nowak, Ulrich and Weyer, J.}, title = {Prognoserechnung zur AIDS-Ausbreitung in der Bundesrepublik Deutschland}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-1511}, number = {SC-94-23}, abstract = {Die Autoren sind sich dar{{\"u}}ber im klaren, daß zahlreiche Imponderabilien die Ergebnisse der vorgelegten Modellrechnungen beeinflussen k{{\"o}}nnen. Immerhin repr{\"a}sentiert jedoch das vorgelegte mathematische Modell die Summe unserer derzeitigen Kenntnisse zur Fragestellung AIDS--Epidemie; neu hinzukommende Erkenntnisse lassen sich rasch einarbeiten und in ihren Konsequenzen {\"u}berschauen. Die Entwicklung neuer effizienter numerischer Methoden spielte eine Schl{\"u}sselrolle bei der tats{\"a}chlichen Simulation dieses umfangreichen realit{\"a}tsnahen mathematischen Modells.}, language = {de} } @misc{DeuflhardLangNowak, author = {Deuflhard, Peter and Lang, Jens and Nowak, Ulrich}, title = {Adaptive Algorithms in Dynamical Process Simulation}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-1823}, number = {SC-95-16}, abstract = {Dynamical simulation of industrially relevant processes strongly advises the use of algorithms, which are {\em adaptive} both in time and in space discretization. The paper presents two alternatives: (a) a fully adaptive method of lines approach, which is based on finite difference methods and essentially applicable to 1D problems; (b) a fully adaptive Rothe method, which is based on a fast multilevel finite element method and applicable to 1D up to 3D.}, language = {en} } @misc{EhrigNowakDeuflhard, author = {Ehrig, Rainald and Nowak, Ulrich and Deuflhard, Peter}, title = {Highly scalable parallel linearly-implicit extrapolation algorithms}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-5405}, number = {TR-96-11}, abstract = {We present parallel formulations of the well established extrapolation algorithms EULSIM and LIMEX and its implementation on a distributed memory architecture. The discretization of partial differential equations by the method of lines yields large banded systems, which can be efficiently solved in parallel only by iterative methods. Polynomial preconditioning with a Neumann series expansion combined with an overlapping domain decomposition appears as a very efficient, robust and highly scalable preconditioner for different iterative solvers. A further advantage of this preconditioner is that all computation can be restricted to the overlap region as long as the subdomain problems are solved exactly. With this approach the iterative algorithms operate on very short vectors, the length of the vectors depends only on the number of gridpoints in the overlap region and the number of processors, but not on the size of the linear system. As the most reliable and fast iterative methods based on this preconditioning scheme appeared GMRES or FOM and BICGSTAB. To further reduce the number of iterations in GMRES or FOM we can reuse the Krylov-spaces constructed in preceeding extrapolation steps. The implementation of the method within the program LIMEX results in a highly parallel and scalable program for solving differential algebraic problems getting an almost linear speedup up to 64 processors even for medium size problems. Results are presented for a difficult application from chemical engineering simulating the formation of aerosols in industrial gas exhaust purification.}, language = {en} } @misc{EhrigNowakDeuflhard, author = {Ehrig, Rainald and Nowak, Ulrich and Deuflhard, Peter}, title = {Massively Parallel Linearly-Implicit Extrapolation Algorithms as a Powerful Tool in Process Simulation.}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-3127}, number = {SC-97-43}, abstract = {We study the parallelization of linearly--implicit extrapolation codes for the solution of large scale PDE systems and differential algebraic equations on distributed memory machines. The main advantage of these algorithms is that they enable adapativity both in time and space. Additive Krylov--Schwarz methods yield high parallel perfomance for such extrapolation methods. Our approach combines a slightly overlapping domain decomposition together with a polynomial block Neumann preconditioner and a reduced system technique. Furthermore we get important advantages through the explicit computation of the matrix--products of the preconditioner and the matrix of the linear system. The parallel algorithms exhibit scalability up to 64 processors already for medium--sized test problems. We show that the codes are really efficient in large application systems for chemical engineering problems.}, language = {en} } @misc{DeuflhardNowakLutzWestphal, author = {Deuflhard, Peter and Nowak, Ulrich and Lutz-Westphal, Brigitte}, title = {Bessel'scher Irrgarten}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-9525}, number = {07-09}, abstract = {Dieser Artikel berichtet {\"u}ber eine erfolgreiche Sch{\"u}leraktivit{\"a}t, die seit Jahren am Zuse-Institut Berlin (ZIB) bei Besuchen von Sch{\"u}lergruppen erprobt und verfeinert worden ist. Das hier zusammengestellte Material ist gedacht als Basis f{\"u}r eine Unterrichtseinheit in Leistungskursen Mathematik an Gymnasien. Inhaltlich wird von einem zwar f{\"u}r Sch{\"u}ler (wie auch Lehrer) neuen, aber leicht fasslichen Gegenstand ausgegangen: der Drei-Term-Rekursion f{\"u}r Besselfunktionen. Die Struktur wird erkl{\"a}rt und in ein kleines Programm umgesetzt. Dazu teilen sich die Sch{\"u}ler selbstorganisierend in Gruppen ein, die mit unterschiedlichen Taschenrechnern "um die Wette" rechnen. Die Sch{\"u}ler und Sch{\"u}lerinnen erfahren unmittelbar die katastrophale Wirkung von an sich kleinen'' Rundungsfehlern, sie landen -- ebenso wie der Supercomputer des ZIB -- im Bessel'schen Irrgarten''. Die auftretenden Ph{\"a}nomene werden mathematisch elementar erkl{\"a}rt, wobei lediglich auf das Konzept der linearen Unabh{\"a}ngigkeit zur{\"u}ckgegriffen wird. Das dabei gewonnene vertiefte Verst{\"a}ndnis fließt ein in die Konstruktion eines klassischen Algorithmus sowie eines wesentlich verbesserten Horner-artigen Algorithmus.}, language = {de} }