In Barnes-Hut, we divide the space into four quadrants. As long as there are a sufficient number o stars in a quadrant, we sub-divide that quadrant into four more quadrants.
To estimate forces on the red particle by all particles in the green box, if L is sufficiently small compared to D ($L/D$), we combine the forces of all particles in the green box and use this combined body to calculate gravitational pull on the red particle.
In Barnes-Hut, we divide the space into four quadrants. As long as there are a sufficient number o stars in a quadrant, we sub-divide that quadrant into four more quadrants.
To estimate forces on the red particle by all particles in the green box, if L is sufficiently small compared to D ($L/D$), we combine the forces of all particles in the green box and use this combined body to calculate gravitational pull on the red particle.
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