Rms value of the y-component of the velocity during the linear-growth phase of the 2D relativistic Kelvin-Helmholtz instability, for different numerical schemes. The solid lines represent the results obtained at the highest resolution, 1024 × 2048, while the dashed lines represent the results obtained at the lowest resolution, 128 × 256. The timestep is chosen so that the CFL factor is C ≈ 0.25 for all of the runs.