Pairs vs. particle count N, as in Fig. 3, but with particle radius s = 2 × 10⁻³au. Orange: number of pairs that needed to be checked in the apoapsis/periapsis filter. Blue: actual number of collision pairs (that could ultimately collide). These determine the runtime and memory for the creation of the collision list; see Table 2. Solid lines: N(N − 1)/2. Dashed line: guideline with a slope of 2.