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| • |
Each
box needs to know
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– |
The
total mass of all the
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particles
that it contains
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The
center-of-mass of all
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the
particles it contains
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This
can be computed
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recursively
(i.e., we can
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compute
the values for box
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B
if we know the values for
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each
of B’s subboxes)
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| • |
Building
the octree must be
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efficient
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– |
The
tree is rebuilt after
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every
time step
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It is
possible for the tree to
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be
badly balanced, requiring
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O(n2)
time to build
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In
practice, tree has height
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of
about O(log n)
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Thus,
tree building takes
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time
O(n log n)
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