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Midwest Symposium on Circuits and Systems (MWSCAS)

作者： M. Yanilmaz V.W. Eveleigh Department of Electrical Engineering and Computer Science Technological Institute Northwestern University Evanston IL USA CASE (Computer Applications in Software Engineering) Center Syracuse University Syracuse NY USA

Static and dynamic numerical device modeling based on dot product evaluation of multidimensional Bernstein polynomial interpolants to evaluate device operating characteristics is presented as an alternative to analytical modeling and table look-up modeling schemes that have been proposed. The model formulation satisfies the requirements imposed by the algebraic-differential equation solution algorithms of most simulators, namely continuity of the output variables and preservation of the monotonicity and concavity or convexity of the data. It is to be noted, however, that those are necessary but not sufficient conditions. Simulator convergence is improved by treating the intrinsic node charges as state variables and using their variations over iteration steps as an iteration criterion along with the node voltage variation checks. MOSFET is taken as a benchmark device. Experimental results to illustrate the effect of the basic premises of the numerical model on simulation performance are presented.< >

关键词： Numerical models Circuit simulation Multidimensional systems Polynomials Analytical models Equations Sufficient conditions Voltage MOSFET circuits Numerical simulation

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Linear Quadratic Tracking Problems in Hilbert Space: Application to Optimal Active Noise Suppression

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IFAC Proceedings Volumes 1989年第4期22卷 5-10页

作者： H.T. Banks S.L. Keeling R.J. Silcox C. Wang Center for Control Sciences Division of Applied Mathematics Brown University Providence RI 02912 USA Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton VA 23665 USA Acousic Division NASA Langley Research Center Hampton VA 23665 USA

In this note we discuss a quadratic tracking problem for systems described by infinite dimensional evolution equations. We present theoretical results for feedback controls as well as general approximation results. Ap...

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CLEER - AN AI-SYSTEM DEVELOPED TO ASSIST EQUIPMENT ARRANGEMENTS ON WARSHIPS

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NAVAL ENGINEERS JOURNAL 1989年第3期101卷 127-137页

作者： ZHOU, HH SILVERMAN, BG SIMKOL, J Dr. H. Harry Zhou:is a research professor at the Institute for Artificial Intelligence of The George Washington University. Dr. Zhou received his master's degree and Ph.D. in computer science from Vanderbilt University in 1984 and 1987 respectively. He did his dissertation in the fields of artificial intelligence analogical reasoning and machine learning. His research interests include: classifier systems genetic algorithms learning by analogy inductive learning adaptive expert systems automated knowledge acquisition and adaption. He is also interested in data base design programming languages mental modeling and software engineering. Dr. Barry G. Silverman:is director of the Institute for Artificial Intelligence and a professor at the Engineering Administration Department of The George Washington University. He is also president of IntelliTek Inc. an AI consulting firm. Dr. Silverman received the B.S.E. M.S.E. and Ph.D. degrees from the University of Pennsylvania. He has been a principal developer of four generic AI products as well as eight AI applications. Since 1979 he has written over 100 papers and reports on these AI efforts. Joel Simkol:is a research scientist currently engaged in designing expert system architectures to support electronic warfare vulnerability analyses threat assessments shipboard topside antenna arrangements and C3countermeasures employment. Mr. Simkol's work in applying expert systems technology to electromagnetic interference and to spectrum management has generated increased interest and participation from all branches of government agencies.

This paper describes a modularized AI system being built to help improve electromagnetic compatibility (EMC) among shipboard topside equipment and their associated systems. CLEER is intended to act as an easy to use integrator of existing expert knowledge and pre-existing data bases and large scale analytical models. Due to these interfaces; to the need for portability of the software; and to artificial intelligence related design requirements (such as the need for spatial reasoning, expert data base management, model base management, track-based reasoning, and analogical (similar ship) reasoning) it was realized that traditional expert system shells would be inappropriate, although relatively off-the-shelf AI technology could be incorporated. In the same vein, the rapid prototyping approach to expert system design and knowledge engineering was not pursued in favor of a rigorous systems engineering methodology. The critical design decisions affecting CLEER's development are summarized in this paper along with lessons learned to date all in terms of “how,” “why,” and “when” specific features are being developed.

关键词： Artificial Intelligence

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TOWARDS DEVELOPING ROBUST ALGORITHMS FOR SOLVING PARTIAL-DIFFERENTIAL EQUATIONS ON MIMD MACHINES

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PARALLEL COMPUTING 1988年第1期6卷 19-44页

作者： SALTZ, JH NAIK, VK Institute for Computer Applications in Science and Engineering Yale University New Haven CT 06520-2158 U.S.A.

Methods are proposed for efficient computation of numerical algorithms on a wide variety of MIMD machines. These techniques reorganize the data dependency patterns so that the processor utilization is imporved. The model problem examined finds the time-accurate solution to a parabolic partial differential equation discretized in space and implicitly marched forward in time. The algorithms investigated are extensions of Jacobi and SOR. The extensions consist of iterating over a window of several timesteps, allowing efficient overlap of computation with communication. The methods suggested here increase the degree to which work can be performed while data are communicated between processors. The effect of the window size and of domain partitioning on the system performance is examined both analytically and experimentally by implementing the algorithm on a simulated multiprocessor system.

关键词： concept of windowing MIMD machines performance results on a simulated multiprocessor-system solving partial differential equations

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Multigrid method for stability problems

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Journal of Scientific Computing 1988年第3期3卷 261-274页

作者： Ta'asan Shlomo Department of Applied Mathematics and Computer Science The Weizmann Institute of Science Rehovot 76100 Israel Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton 23665 Virginia United States

The problem of calculating the stability of steady state solutions of differential equations is treated. Leading eigenvalues (i.e., having maximal real part) of large matrices that arise from discretization are to be calculated. An efficient multigrid method for solving these problems is presented. The method begins by obtaining an initial approximation for the dominant subspace on a coarse level using a damped Jacobi relaxation. This proceeds until enough accuracy for the dominant subspace has been obtained. The resulting grid functions are then used as an initial approximation for appropriate eigenvalue problems. These problems are solved first on coarse levels, followed by refinement until a desired accuracy for the eigenvalues has been achieved. The method employs local relaxation on all levels together with a global change on the coarsest level only, which is designed to separate the different eigenfunctions as well as to update their corresponding eigenvalues. Coarsening is done using the FAS formulation in a nonstandard way in which the right-hand side of the coarse grid equations involves unknown parameters to be solved for on the coarse grid. This in particular leads to a new multigrid method for calculating the eigenvalues of symmetric problems. Numerical experiments with a model problem that are presented demonstrate the effectiveness of the method proposed. Using an FMG algorithm a solution to the level of discretization errors is obtained in just a few work units (less than 10), where a work unit is the work involved in one Jacobi relaxation on the finest level. © 1988 Plenum Publishing Corporation.

关键词： Multigrid relaxation methods stability problems

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Accurate multigrid solution of the euler equations on unstructured and adaptive meshes

Accurate multigrid solution of the euler equations on unstru...

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1st National Fluid Dynamics Conference, 1988

作者： Mavriplis, Dimitri J. Institute for Computer Applications in Science and Engineering NASA Langley Research Center HamptonVA United States

A method for accurately solving inviscid compressible flow in the subcritical and supercritical regimes about complex configurations is presented. The method is based on the use of unstructured triangular meshes in two dimensions, and special emphasis is placed on the accuracy and efficiency of the solutions. High accuracy is achieved by careful scaling of the artificial dissipation terms, and by reformulating the inner and outer boundary conditions for both the convective and dissipative operators. An adaptive grid refinement strategy is presented which enhances the solution accuracy for complex flows. When coupled with an unstructured multigrid algorithm, this method is shown to produce an efficient solver for flows about arbitrary configurations. © 1988 by the American institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Computational fluid dynamics

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Overview and extensions of a system for routing directed graphs on SIMD architectures

Overview and extensions of a system for routing directed gra...

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Frontiers of Massively Parallel Computation

作者： S. Tomboulian NASA Langley Research Center Institute for Computer Applications in Science and Engineering Hampton VA USA

A method is given for parallelizing the problems of directed graphs on a single-instruction multiple-data (SIMD) machine model that uses only nearest-neighbor connections for communication and has no facility for local indirect addressing. Each vertex of the graph is assigned to a processor in the machine. Rules for labeling are introduced that support the use of a simple algorithm for movement of data along the edges of the graph. Additional algorithms are defined for addition and deletion of edges. Modifying or adding a new edge takes the same time as parallel traversal. This combination of architecture and algorithm defines a system that is relatively simple to build and can do fast graph processing. All edges can be traversed in parallel in time O(T), where T is empirically proportional to the average path length in the embedding times the average degree of the graph. An extension to the above method is presented which allows for enhanced performance by allowing some broadcasting capabilities.< >

关键词： Routing Labeling computer architecture NASA computer applications Data engineering Nearest neighbor searches Broadcasting Parallel processing Multiprocessor interconnection networks

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Parameter estimation technique for boundary value problems by spline collocation method

Parameter estimation technique for boundary value problems b...

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IEEE Conference on Decision and Control

作者： F. Kojima Institute of Computer Applications in Science and Engineering NASA-Langley Research Center Hampton VA USA

A parameter estimation technique for boundary integral equations of the second kind is developed. The output least-squares-identification technique using the spline collocation method is considered. The convergence analysis for the numerical method is discussed. The results are applied to boundary parameter estimations for two-dimensional Laplace and Helmholtz equations.< >

关键词： Parameter estimation Boundary value problems Spline Integral equations Least squares methods Mathematical model computer applications NASA Convergence of numerical methods Laplace equations

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Automatically generated acceptance test: a software reliability experiment

Automatically generated acceptance test: a software reliabil...

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Workshop on Software Testing, Verification, and Analysis

作者： P.W. Protzel Institute for Computer Applications in Science and Engineering NASA-Langley Research Center Hampton VA USA

The author presents results of a software reliability experiment that investigates the feasibility of a new error detection method. The method can be used as an acceptance test and is solely based on empirical data about the behavior of internal states of a program. The experimental design uses the existing environment of a multiversion experiment and used the launch interceptor problem as a model problem. This allows the controlled experimental investigation of versions with well-known single and multiple faults, and the availability of an oracle permits the determination of the error detection performance of the test. Fault-interaction phenomena are observed that have an amplifying effect on the number of error occurrences. Preliminary results indicate that all faults examined so far are detected by the acceptance test. This shows promise for further investigations and for the use of this test method in other applications.< >

关键词： Automatic testing Software testing Software reliability NASA Fault detection Application software Costs computer applications Reliability engineering computer errors

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Spectral solution of the incompressible Navier-Stokes equations on the Connection Machine 2

Spectral solution of the incompressible Navier-Stokes equati...

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Supercomputing Conference

作者： S. Tomboulian C. Streett M. Macaraeg Institute for Computer Applications in Science and Engineering (ICASE) NASA-Langley Research Center Hampton VA USA NASA-Langley Research Center USA

The authors address the issue of solving the time-dependent incompressible Navier-Stokes equations on the Connection Machine 2, for the problem of transition to turbulence on the steady flow in a channel. The spectral algorithm used serially requires O(N/sup 4/) operations; using the massive parallelism of the CM it becomes an O(N/sup 2/) problem, then solving the equations on an N*N*N grid. Preliminary timings of the code, written in Lisp, are included and compared with a corresponding code optimized for the Cray-2 for a 128*128*101 grid.< >

关键词： Navier-Stokes equations NASA Kernel Fluid dynamics Postal services Timing Computational modeling Physics Supercomputers Parallel processing

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