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Abstract: We discuss the performance characteristics of using the modification of thetree code suggested by Barnes \citep{1990JCoPh

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161B} in the context of theTreePM code. The optimisation involves identifying groups of particles andusing only one tree walk to compute force for all the particles in the group.This modification has been in use in our implementation of the TreePM code forsome time, and has also been used by others in codes that make use of treestructures. In this paper, we present the first detailed study of theperformance characteristics of this optimisation. We show that themodification, if tuned properly can speed up the TreePM code by a significantamount. We also combine this modification with the use of individual time stepsand indicate how to combine these two schemes in an optimal fashion. We findthat the combination is at least a factor of two faster than the modifiedTreePM without individual time steps. Overall performance is often faster by alarger factor, as the scheme of groups optimises use of cache for largesimulations.



Author: Nishikanta Khandai, J. S. Bagla

Source: https://arxiv.org/







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