Comparison between simulations and analytical predictions for F_x (left panels) and F_y (right panels) slightly beyond first shell-crossing time. From top to bottom, we consider Q1D-2SIN, ANI-2SIN, Q1D-3SIN, and ANI-3SIN initial conditions, respectively. For each initial condition, we present the force for three different values of y and/or z, as indicated in each panel. The largest values of y and z are outside the multi-stream region. The dots stand for the measurements in the ColDICE simulations. The solid green curves in the left panels give the theoretical prediction for F_x from the analytical formula (51). The solid blue lines correspond to the theoretical predictions for F_x and F_y obtained from the LPT acceleration using Eq. (49) (only in the multi-stream region) and Eq. (15), respectively. The dashed orange lines represent the force field resulting from solving the Poisson Eq. (14), when using the LPT displacement instead of the supposedly exact positions of particles in the ColDICE runs.