Symmetry of force on particles: Fij = -Fji (Newton's Law of Action and Reaction!)
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only half need to be computed
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Sequentially this can easily be taken into account for one just does loops with sum over particles i, and then sums for force calculation over particles j <= i and then calculate algebraic form of Fij and then accumulates -- Force on i increments by Fij and Force on j decrements by Fij
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Parallel version has two issues -- firstly one cannot use "owner-computes" rule directly and secondly one must worry about load blancing
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Assuming for example that processors
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assigned with block distribution in
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column direction.
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To calculate the force between
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2 particles will take N/Nproc iterations
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in the longest running processor
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