Free-energy U (normalized to its initial value U₀) during the collision of Alfvén wave packets on numerical meshes (2D/3D) of various resolutions (indicated by different line styles). Top: evolution of U₀/U for the set of 2D models. Slopes for the asymptotic linear relation between U₀/U and ln t are indicated by dashed/dotted lines, comparing to Fig. 7 of Li et al. (2019). Bottom: free-energy evolution normalized to U₀ comparing to Figs. 2 and 5 from Li et al. (2019). The asymptotic slope for 3D models found by Li et al. (2019) is indicated by a gray dashed line for reference.