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The Global ETD Search service is a free service for researchers
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Showing 21 to 27 of 27 (0.123 seconds)Spelling suggestions: "subject:"computational escience"" "subject:"computational ascience""
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ALGORITHMS FOR DEGREE-CONSTRAINED SUBGRAPHS AND APPLICATIONSS M Ferdous (11804924) 19 December 2021 (has links)
A degree-constrained subgraph construction (DCS) problem aims to find an optimal spanning subgraph (w.r.t an objective function) subject to certain degree constraints on the vertices. DCS generalizes many combinatorial optimization problems such as Matchings and Edge Covers and has many practical and real-world applications. This thesis focuses on DCS problems where there are only upper and lower bounds on the degrees, known as b-matching and b-edge cover problems, respectively. We explore linear and submodular functions as the objective functions of the subgraph construction.<br><br>The contributions of this thesis involve both the design of new approximation algorithms for these DCS problems, and also their applications to real-world contexts.<br>We designed, developed, and implemented several approximation algorithms for DCS problems. Although some of these problems can be solved exactly in polynomial time, often these algorithms are expensive, tedious to implement, and have little to no concurrency. On the contrary, many of the approximation algorithms developed here run in nearly linear time, are simple to implement, and are concurrent. Using the local dominance framework, we developed the first parallel algorithm submodular b-matching. For weighted b-edge cover, we improved the classic Greedy algorithm using the lazy evaluation technique. We also propose and analyze several approximation algorithms using the primal-dual linear programming framework and reductions to matching. We evaluate the practical performance of these algorithms through extensive experimental results.<br><br>The second contribution of the thesis is to utilize the novel algorithms in real-world applications. We employ submodular b-matching to generate a balanced task assignment for processors to build Fock matrices in the NWChemEx quantum chemistry software. Our load-balanced assignment results in a four-fold speedup per iteration of the Fock matrix computation and scales to 14,000 cores of the Summit supercomputer at Oak Ridge National Laboratory. Using approximate b-edge cover, we propose the first shared-memory and distributed-memory parallel algorithms for the adaptive anonymity problem. Minimum weighted b-edge cover and maximum weight b-matching are shown to be applicable to constructing graphs from datasets for machine learning tasks. We provide a mathematical optimization framework connecting the graph construction problem to the DCS problem.
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A Multi-Physics Software Framework on Hybrid Parallel Computing for High-Fidelity Solutions of Conservation LawsChen, Yung-Yu 27 September 2011 (has links)
No description available.
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A comparison of two multilevel Schur preconditioners for adaptive FEMKarlsson, Christian January 2014 (has links)
There are several algorithms for solving the linear system of equations that arise from the finite element method with linear or near-linear computational complexity. One way is to find an approximation of the stiffness matrix that is such that it can be used in a preconditioned conjugate residual method, that is, a preconditioner to the stiffness matrix. We have studied two preconditioners for the conjugate residual method, both based on writing the stiffness matrix in block form, factorising it and then approximating the Schur complement block to get a preconditioner. We have studied the stationary reaction-diffusion-advection equation in two dimensions. The mesh is refined adaptively, giving a hierarchy of meshes. In the first method the Schur complement is approximated by the stiffness matrix at one coarser level of the mesh, in the second method it is approximated as the assembly of local Schur complements corresponding to macro triangles. For two levels the theoretical bound of the condition number is 1/(1-C²) for either method, where C is the Cauchy-Bunyakovsky-Schwarz constant. For multiple levels there is less theory. For the first method it is known that the condition number of the preconditioned stiffness matrix is O(l²), where l is the number of levels of the preconditioner, or, equivalently, the number mesh refinements. For the second method the asymptotic behaviour is not known theoretically. In neither case is the dependency of the condition number of C known. We have tested both methods on several problems and found the first method to always give a better condition number, except for very few levels. For all tested problems, using the first method it seems that the condition number is O(l), in fact it is typically not larger than Cl. For the second method the growth seems to be superlinear.
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[en] SCIENCE AS A GAME: PLAYFUL APPROACHES TO SCIENTIFIC SOFTWARE INTERFACE DESIGN / [pt] A CIÊNCIA COMO JOGO: ABORDAGENS LÚDICAS AO DESIGN DE INTERFACES PARA SOFTWARE CIENTÍFICOFRANCISCO OLIVEIRA DE QUEIROZ 03 July 2019 (has links)
[pt] De grande importância para pesquisa científica, o software científico se mostra, por vezes, desafiador no que se refere ao design de interfaces com o usuário. Por outro lado, a gamificação se oferece como potencial solução em questões de experiência com o usuário e interatividade. Nesta tese, desenvolvemos um método para a gamificação de software científico voltado para processos de design colaborativo, orientado por um modelo baseado em jogo, informado por aspectos de uso e desenvolvimento deste tipo de software e, também, por aspectos similares ao jogo na prática científica. / [en] Vastly important to scientific research, scientific software is often challenging regarding the design of its user interfaces. On the other hand, gamification is seen as a potential solution in matters of user experience and interactivity. In this thesis, we develop a method for the gamification of scientific software aimed at collaborative design processes, guided by a game-based model, informed by aspects of use and development of that type of software and, also by game-like aspects of scientific practice.
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Numerical simulation of acoustic wave propagation with a focus on modeling sediment layers and large domainsEstensen, Elias January 2022 (has links)
In this report, we study how finite differences can be used to simulate acoustic wave propagation originating from a point source in the ocean using the Helmholtz equation. How to model sediment layers and the vast size of the ocean is studied in particular. The finite differences are implemented with summation by parts operators with boundary conditions enforced with simultaneous approximation terms and projection. The numerical solver is combined with the WaveHoltz method to improve the performance. Sediment layers are handled with interface conditions and the domain is artificially expanded using absorbing layers. The absorbing layer is implemented with an alternative approach to the super-grid method where the domain expansion is accomplished by altering the wave speed rather than with coordinate transformations. To isolate these issues, other parameters such as variations in the ocean floor are neglected. With this simplification, cylindrical coordinates are used and the angular variation is assumed to be zero. This reduces the problem to a quasi-three-dimensional system. We study how the parameters of the alternative absorbing layer approach affect its quality. The numerical solver is verified on several test cases and appears to work according to theory. Finally, a semi-realistic simulation is carried out and the solution seems correct in this setting.
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TU-Spektrum 2/2004, Magazin der Technischen Universität ChemnitzSteinebach, Mario, Friebel, Alexander, Häckel-Riffler, Christine, Tzschucke, Volker, Pollmer, Caroline, Horst, Gabriela, Brabandt, Antje, Reichold, Kathrin 15 December 2004 (has links) (PDF)
zweimal im Jahr erscheinende Zeitschrift über aktuelle Themen der TU Chemnitz, ergänzt von Sonderheft(en)
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TU-Spektrum 2/2004, Magazin der Technischen Universität ChemnitzSteinebach, Mario, Friebel, Alexander, Häckel-Riffler, Christine, Tzschucke, Volker, Pollmer, Caroline, Horst, Gabriela, Brabandt, Antje, Reichold, Kathrin 15 December 2004 (has links)
zweimal im Jahr erscheinende Zeitschrift über aktuelle Themen der TU Chemnitz, ergänzt von Sonderheft(en)
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