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Nonreflecting Boundary Conditions for Elastodynamic Scattering
(1999)SAM Research ReportAn exact nonreflecting boundary condition was derived previously for time-dependent elastic waves in three space dimensions [1]. It is local in time, nonlocal on the artificial boundary, and involves only first derivatives of the displacement. Here it is shown how to combine that boundary condition with finite difference and finite element methods. Stability issues are discussed. Numerical examples demonstrate the high improvement in ...Report -
Accuracy of Two Three-term and Three Two-term Recurrences for Krylov Space Solvers
(1999)SAM Research ReportIt has been widely observed that Krylov space solvers based on two three-term recurrences can give significantly less accurate residuals than mathematically equivalent solvers implemented with three two-term recurrences. In this paper we attempt to clarify and justify this difference theoretically by analyzing the gaps between recursively and explicitly computed residuals. It is shown that, in contrast with the two-term recurrences analyzed ...Report -
CoFrame: a modular co-design framework for heterogeneous distributed systems
(1999)TIK ReportThis paper presents CoFrame, a novel modular co-design framework for heterogeneous distributed systems. The center of the approach is a pool of dynamic data structures which is analyzed, modified and refined by algorithms and tools to map a system specification to a feasible implementation consisting of arbitrary linked processors, DSPs and FPGAs. Due to its modular structure, CoFrame can be easily adapted to various control and data flow ...Report -
Residual smoothing techniques: do they improve the limiting accuracy of iterative solvers?
(1999)SAM Research ReportMany iterative methods for solving linear systems, in particular the biconjugate gradient (BICG) method and its "squared" version CGS(orBICGS), produce often residuals whose norms decrease far from monotonously, but fluctuate rather strongly. Large intermediate residuals are known to reduce the ultimately attainable accuracy of the method, unless special measures are taken to counteract this effect. One measure that has been suggested ...Report -
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Fully Discrete hp-Finite Elements: Fast Quadrature
(1999)SAM Research ReportA fully discrete hp finite element method is presented. It combines the features of the standard hp finite element method (conforming Galerkin Formulation, variable order quadrature schemes, geometric meshes, static condensation) and of the spectral element method (special shape functions and spectral quadrature techniques). The speed-up (relative to standard hp elements) is analyzed in detail both theoretically and computationally .Report -
A service management toolkit for active networks
(1999)TIK ReportActive networking, where network nodes perform customized processing of packets, is a rapidly expanding field of research. This paper investigates the realization of service management on a Virtual Active Network (VAN), the key concept in our active network management framework [11]. A VAN can be seen as a thin (software) layer in an active networking environment, which creates a generic service abstraction, offered by the provider to the ...Report -
Fuzzy decision diagrams for the representation, analysis, and optimization of rule bases
(1999)TIK ReportWhen no expert knowledge is available, fuzzy if-then rules may be extracted from examples of performance of a system. For this, an a priori decision on the number of linguistic terms of the linguistic variables may be required. This may induce a "rigid granularity", usually finer than that actually required by the system. Fuzzy decision diagrams (FuDDs) are introduced as an efficient data structure to represent fuzzy rule bases and to ...Report -
Virtualizing active networks for Telecom environments
(1999)TIK ReportThe paper addresses the question on how the benefits of active networking, such as customized packet processing inside the network and flexible service management, can be realized in a telecom environment. More precisely, we ask: How can a network provider, whose infrastructure is based on active networking technology, support a large number of customers, all of which independently install and run their own customized active services in ...Report