Normalised amplitude of the largest mode of the shearing box (a sinusoid with a wavenumber K=(30, 0, 30)^T) for different numbers of dust species and sampling methods. The runs with ten dust species are shown in blue, 20 dust species are shown in orange, and 40 dust species are shown in green. The solid line indicates the GL method (27), and the dotted line indicates a log-linear sampling method (runs: PSI20, PSI10, PSI40_disc., PSI20_disc., and PSI10_disc..). The dot-dashed line is an analytical solution of the growth rate calculated with psitools.