To improve numerical stability still further, some additional measures are also implemented here. Consider, as an example, a Gaussian wavepacket, for which the quantum force is linear in x. Clearly, Eq. ( ) yields more accurate F Q values in the interior of the wavepacket than in the periphery, since the trajectories are less densely distributed in regions of low density. Numerical errors near the edges do not necessarily lead to a significant deterioration of the overall propagation, however-again, because probabilities are small in the periphery. If the edge errors are stable at least (even if somewhat large) then as discussed, comparatively large errors at the periphery have little effect in the interior. In any event, errors tend to manifest as trajectories that oscillate around their true course. Numerical instability is signalled by oscillations that grow in magnitude over time, and/or propagate into the interior region.