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 mo...
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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.
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 ...
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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 tw...
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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 loca...
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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.< >
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 an...
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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.< >
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 ab...
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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.< >
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...
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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.< >
Problems on the identification of two-dimensional spatial domains arising in the detection and characterization of structural flaws in materials are considered. For a thermal diffusion system with external boundary in...
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Problems on the identification of two-dimensional spatial domains arising in the detection and characterization of structural flaws in materials are considered. For a thermal diffusion system with external boundary input, observations of the temperature on the surface are used in an output least square approach. Parameter estimation techniques based on the method of mappings are discussed, and approximation schemes are developed based on a finite-element Galerkin approach. Theoretical convergence results for computational techniques are given, and the results are applied to the identification of two kinds of boundary shapes.< >
作者：
SHIH, KGNASA
Langley Research Center Institute for Computer Applications in Science and Engineering Hamp
We establish the existence of concave solutions of Berman’s equation which describes the laminar flow in channels with injection through porous walls. It is found that the (unique) concave solutions exist for all inj...
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We establish the existence of concave solutions of Berman’s equation which describes the laminar flow in channels with injection through porous walls. It is found that the (unique) concave solutions exist for all injection Reynolds number R<0.
A compact difference scheme derived in (Phillips and Rose, SIAM J. Statist. Comput. 7 , 288 (1986)) for treating the equilibrium equations of elasticity is studied. The scheme truns out to be inconsistent and unstable...
A compact difference scheme derived in (Phillips and Rose, SIAM J. Statist. Comput. 7 , 288 (1986)) for treating the equilibrium equations of elasticity is studied. The scheme truns out to be inconsistent and unstable. A multigrid method which takes into account these properties is described. The solution of the discrete equations, up to the level of discretization errors, is obtained by this method in just 16 work units, where a work unit is the work involved in relaxing the finest grid equations once.
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