114,342 research outputs found

    Hybrid Spectral Difference/Embedded Finite Volume Method for Conservation Laws

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    A novel hybrid spectral difference/embedded finite volume method is introduced in order to apply a discontinuous high-order method for large scale engineering applications involving discontinuities in the flows with complex geometries. In the proposed hybrid approach, the finite volume (FV) element, consisting of structured FV subcells, is embedded in the base hexahedral element containing discontinuity, and an FV based high-order shock-capturing scheme is employed to overcome the Gibbs phenomena. Thus, a discontinuity is captured at the resolution of FV subcells within an embedded FV element. In the smooth flow region, the SD element is used in the base hexahedral element. Then, the governing equations are solved by the SD method. The SD method is chosen for its low numerical dissipation and computational efficiency preserving high-order accurate solutions. The coupling between the SD element and the FV element is achieved by the globally conserved mortar method. In this paper, the 5th-order WENO scheme with the characteristic decomposition is employed as the shock-capturing scheme in the embedded FV element, and the 5th-order SD method is used in the smooth flow field. The order of accuracy study and various 1D and 2D test cases are carried out, which involve the discontinuities and vortex flows. Overall, it is shown that the proposed hybrid method results in comparable or better simulation results compared with the standalone WENO scheme when the same number of solution DOF is considered in both SD and FV elements.Comment: 27 pages, 17 figures, 2 tables, Accepted for publication in the Journal of Computational Physics, April 201

    Scalable Task-Based Algorithm for Multiplication of Block-Rank-Sparse Matrices

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    A task-based formulation of Scalable Universal Matrix Multiplication Algorithm (SUMMA), a popular algorithm for matrix multiplication (MM), is applied to the multiplication of hierarchy-free, rank-structured matrices that appear in the domain of quantum chemistry (QC). The novel features of our formulation are: (1) concurrent scheduling of multiple SUMMA iterations, and (2) fine-grained task-based composition. These features make it tolerant of the load imbalance due to the irregular matrix structure and eliminate all artifactual sources of global synchronization.Scalability of iterative computation of square-root inverse of block-rank-sparse QC matrices is demonstrated; for full-rank (dense) matrices the performance of our SUMMA formulation usually exceeds that of the state-of-the-art dense MM implementations (ScaLAPACK and Cyclops Tensor Framework).Comment: 8 pages, 6 figures, accepted to IA3 2015. arXiv admin note: text overlap with arXiv:1504.0504

    Communication, coordination and networks

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    We study experimentally how the network structure and length of pre-play communication affect behavior and outcome in a multi-player coordination game with conflicting preferences. Network structure matters but the interaction between network and time effects is more subtle. Under each time treatment, substantial variations are observed in both the rate of coordination and distribution of coordinated outcomes across networks. But, increasing the communication length improves both efficiency and equity of coordination. In all treatments, coordination is mostly explained by convergence in communication. We also identify behaviors that explain variations in the distribution of coordinated outcomes both within and across networks

    Mr. Justice Posner? Unpacking the Statistics

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    The Pricing of Non-Price Terms in Sovereign Bonds: The Case of the Greek Guarantees

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    In March 2012, Greece conducted one of the biggest and most brutal sovereign debt restructurings ever, asking holders of Greek government bonds to take net present value haircuts of near 80 percent. Greece forced acquiescence to its terms from a large number of its bonds by using a variety of legal strong-arm tactics. With the vast majority of Greek bonds, the tactics worked. There were, however, thirty-six bonds guaranteed by the Greek state, which, because of the weakness of the underlying companies, were effectively obligations of the Greek state. Yet, on these thirty six bonds, even though Greece desperately needed every euro of respite it could get, no restructuring was even attempted. Why not? The answer we received was that the guarantees escaped the restructuring because their contractual provisions made them much harder to restructure than the ordinary Greek government bonds. Assuming this contract-based claim to be true, the foregoing, in combination with the Euro area crisis of 2010–2014 throws up an opportunity to test the extent to which markets price legal differences in bond contract terms. We report evidence that the markets did price in at least some of the advantage that guaranteed bonds had over ordinary sovereign bonds in the months immediately prior to the March 2012 restructuring
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