Distribution of the sonic Mach number in the simulations of the Kelvin-Helmholtz instability at t/t_max = 1/6 for different values of the initial magnetic field, Β_x, computed as , with α = (0.1, 0.2, 0.5, 0.6, 0.7, 0.9, 0.9, 1.0, 1.2). These simulations were performed on a 512 × 256 grid with M_x = 10⁻³. The title in each panel is the corresponding minimum Alfvén Mach number of the flow at t = 0. For a strong enough initial magnetic field, the magnetic stresses prevent the growth of the instability.