Further analysis of the RPMC simulation of the grains-and-boulders model: (a) contributions to dN_B/dt: dN_g→B/dt (solid curve), −dN_B→B/dt (dashed curve); (b) statistics of final boulder mass as a function of RP count n: standard deviation of the mean over 10 runs (error bars) and physical spread (filled area). Simulation parameters as in Fig. 8. In (a), the full n = 1 792 RPs were used; in (b), the number of RPs was varied. n was divided into n_B boulder-mass RPs and n_g = 6n_B grain-mass RPs with equal-weight swarms, M_i = M_j∀i, j ∈ {1, …, n}. The horizontal black line indicates the expected final boulder mass .