Solution of 1D heat diffusion equation with β-dependent suppression of thermal diffusivity (Eq. C.2). From left to right: Initial solution at time t = 0, final solution at time t = 0.1, and zoomed-in view of the final solution in the region 0.22 < x < 0.27. The times are in units of L²/χ₀. The different lines correspond to the solution obtained with a finite difference code without and with harmonic filtering (green and dark red, respectively), while the SNOOPY solution is shown in blue (without filtering) and gold (with filtering). In the rightmost panel the bar plots show their relative error compared to the finite-difference solution with harmonic filter. The addition of harmonic filtering renders SNOOPY more diffusive, but eliminates the problem of Gibbs oscillations at the grid-scale.