Parallelism is clear -- update particles in parallel but what about communication?
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It requires a thoughtful algorithm but can efficiently fetch information needed.
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Fetch all the information needed by ANY particle in a given processor as multipole approach implies that particles tend to need same long range components if nearby
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call this "locally essential" data
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cf. O(N) multipole-multipole approach
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Effectively top of tree replicated in all processors and they just differ near bottom which is expanded in a way that depends on where processor is
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