The simulation volume is usually divided up into cubic cells via an octree ( in a three-dimensional space ), so that only particles from nearby cells need to be treated individually, and particles in distant cells can be treated as a single large particle centered at the cell's center of mass ( or as a low-order multipole expansion ).
12.
In "'tree methods "', such as a Barnes Hut simulation, an octree is usually used to divide the volume into cubic cells in, so that only particles from nearby cells need to be treated individually, and particles in distant cells can be treated as a single large particle centered at the cell's center of mass ( or as a low-order multipole expansion ).
