  Integrations in fixed N-body realisations of smooth density distributions
corresponding to a chaotic galactic potential can be used to derive reliable
estimates of the largest (finite time) Lyapunov exponent X_S associated with an
orbit in the smooth potential generated from the same initial condition, even
though the N-body orbit is typically characterised by an N-body exponent X_N >>
X_S. This can be accomplished either by comparing initially nearby orbits in a
single N-body system or by tracking orbits with the same initial condition
evolved in two different N-body realisations of the same smooth density.
