This expression can be numerically computed using the strategy introduced by Enss et al. Numerical simulations were performed on an ensemble of spins located on a regularly spaced cubic lattice, with the shape of either a thin disk (21 × 21 × 7 grid points) or an elongated cylinder (11 × 11×21 grid points). In order to avoid numerical artifacts due to the periodicity induced by the FFT, zero padding was applied. Satisfactory conditions were obtained by increasing the padding dimensions in test simulations until no significant changes on computed magnetization trajectories were observed. The retained padding was 100 × 100 × 150 padding in the x, y, and z dimensions for all simulations. Finally, because of the singularity at k = 0 this component was computed from the average magnetization. Equations 10 were numerically solved using explicit Runge-Kutta method of order 8 implemented in Scipy by the scipy.integrate.solve ivp adaptive stepsize integrator. The simulations shown in this article were run on a on 10-core Dell Precision 5820 desktop computer.