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  • 1995-1999  (5)
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  • 1
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    Spectral ordering techniques for incomplete LU preconditoners for CG methods (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effectiveness of an incomplete LU (ILU) factorization as a preconditioner for the conjugate gradient method can be highly dependent on the ordering of the matrix rows during its creation. Detailed justification for two heuristics commonly used in matrix ordering for anisotropic problems is given. The bandwidth reduction and weak connection following heuristics are implemented through an ordering method based on eigenvector computations. This spectral ordering is shown to be a good representation of the heuristics. Analysis and test cases in two and three dimensional diffusion problems demonstrate when ordering is important, and when an ILU decomposition will be ordering insensitive. The applicability of the heuristics is thus evaluated and placed on a more rigorous footing.
    Keywords: NUMERICAL ANALYSIS
    Type: NASA-CR-199548 , NIPS-95-05576 , NAS 1.26:199548 , RIACS-TR-95-20
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Unstructured Adaptive Grid Computations on an Array of SMPs (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Dynamic load balancing is necessary for parallel adaptive methods to solve unsteady CFD problems on unstructured grids. We have presented such a dynamic load balancing framework called JOVE, in this paper. Results on a four-POWERnode POWER CHALLENGEarray demonstrated that load balancing gives significant performance improvements over no load balancing for such adaptive computations. The parallel speedup of JOVE, implemented using MPI on the POWER CHALLENCEarray, was significant, being as high as 31 for 32 processors. An implementation of JOVE that exploits 'an array of SMPS' architecture was also studied; this hybrid JOVE outperformed flat JOVE by up to 28% on the meshes and adaption models tested. With large, realistic meshes and actual flow-solver and adaption phases incorporated into JOVE, hybrid JOVE can be expected to yield significant advantage over flat JOVE, especially as the number of processors is increased, thus demonstrating the scalability of an array of SMPs architecture.
    Keywords: Computer Programming and Software
    Type: NASA-CR-202183 , NAS 1.26:202183 , RIACS-TR-96-13 , Parallel CFD 1996 Conference; May 20, 1996 - May 23, 1996; Capri; Italy|Proceedings of Parallel CFD 1996
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Impact of Load Balancing on Unstructured Adaptive Grid Computations for Distributed-Memory Multiprocessors (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The computational requirements for an adaptive solution of unsteady problems change as the simulation progresses. This causes workload imbalance among processors on a parallel machine which, in turn, requires significant data movement at runtime. We present a new dynamic load-balancing framework, called JOVE, that balances the workload across all processors with a global view. Whenever the computational mesh is adapted, JOVE is activated to eliminate the load imbalance. JOVE has been implemented on an IBM SP2 distributed-memory machine in MPI for portability. Experimental results for two model meshes demonstrate that mesh adaption with load balancing gives more than a sixfold improvement over one without load balancing. We also show that JOVE gives a 24-fold speedup on 64 processors compared to sequential execution.
    Keywords: Computer Programming and Software
    Type: NASA-CR-202185 , NAS 1.26:202185 , RIACS-TR-96-15 , IEEE Symposium on Parallel and Distributed Processing; Oct 23, 1996 - Oct 26, 1996; New Orleans, Louisiana; United States|Proceedings of 8th IEEE Symposium on Parallel and Distributed Processing
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  • 4
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    HARP: A Dynamic Inertial Spectral Partitioner (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Partitioning unstructured graphs is central to the parallel solution of computational science and engineering problems. Spectral partitioners, such recursive spectral bisection (RSB), have proven effecfive in generating high-quality partitions of realistically-sized meshes. The major problem which hindered their wide-spread use was their long execution times. This paper presents a new inertial spectral partitioner, called HARP. The main objective of the proposed approach is to quickly partition the meshes at runtime in a manner that works efficiently for real applications in the context of distributed-memory machines. The underlying principle of HARP is to find the eigenvectors of the unpartitioned vertices and then project them onto the eigerivectors of the original mesh. Results for various meshes ranging in size from 1000 to 100,000 vertices indicate that HARP can indeed partition meshes rapidly at runtime. Experimental results show that our largest mesh can be partitioned sequentially in only a few seconds on an SP2 which is several times faster than other spectral partitioners while maintaining the solution quality of the proven RSB method. A parallel WI version of HARP has also been implemented on IBM SP2 and Cray T3E. Parallel HARP, running on 64 processors SP2 and T3E, can partition a mesh containing more than 100,000 vertices into 64 subgrids in about half a second. These results indicate that graph partitioning can now be truly embedded in dynamically-changing real-world applications.
    Keywords: Computer Systems
    Type: NASA-CR-204489 , NAS 1.26:204489 , RIACS-TR-97-01 , Parallel Algorithms and Architectures; Jun 22, 1997 - Jun 25, 1997; Newport, RI; United States
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  • 5
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    Impact of Load Balancing on Unstructured Adaptive Grid Computations for Distributed-Memory Multiprocessors (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The computational requirements for an adaptive solution of unsteady problems change as the simulation progresses. This causes workload imbalance among processors on a parallel machine which, in turn, requires significant data movement at runtime. We present a new dynamic load-balancing framework, called JOVE, that balances the workload across all processors with a global view. Whenever the computational mesh is adapted, JOVE is activated to eliminate the load imbalance. JOVE has been implemented on an IBM SP2 distributed-memory machine in MPI for portability. Experimental results for two model meshes demonstrate that mesh adaption with load balancing gives more than a sixfold improvement over one without load balancing. We also show that JOVE gives a 24-fold speedup on 64 processors compared to sequential execution.
    Keywords: Computer Systems
    Type: NASA-TM-112034 , NAS 1.15:112034 , NAS-96-012 , IEEE Symposium on Parallel and Distributed Processing (SPDP''96); Oct 23, 1996 - Oct 26, 1996; New Orleans, LA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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