Symmetry of force on particles: Fij = -Fji (Newton's Law of Action and Reaction!)
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only half need to be computed so should use triangular arrays
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i.e. just do loops with sum over particles i, sum over particles j <= i and then calculate algebraic form of Fij and then accumulate
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Force on i increments by Fij
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Force on j decrements by Fij
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There is a Load balancing problem with triangular arrays
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Assuming for example that processors assigned with block distribution in column direction.
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To calculate the force between 2 particles
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will take N/Nproc iterations in the
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longest running processor
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i.e. you don't get factor of two back!
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