  The energy diffusion coefficients D_n(E) (n=1,2) for a system of equal mass
particles moving self-consistently in an N-body realisation of a King model are
computed from the probability per unit time, P(E, Delta E), that a star with
initial energy E will undergo an energy change Delta E. In turn, P is computed
from the number of times during the simulation that a particle in a state of
given energy undergoes a transition to another state. These particle states are
defined directly from the time evolution of E by identifying them with the
event occuring between two local maxima in the E(t) curve. If one assumes next
that energy changes are uncorrelated between different states, one can use
diffusion theory to compute D_n(E). The simulations employ N=512, 2048,... ,
32768 particles and are performed using an implementation of Aarseth's direct
integrator N-body1 on a massively parallel computer. The more than seven
million transitions measured in the largest N simulation provide excellent
statistics. The numerically determined D(E)'s are compared against their
theoretical counterparts which are computed from phase-space averaged rates of
energy change due to independent binary encounters. The overall agreement
between them is impressive over most of the energy range, notwithstanding the
very different type of approximations involved, giving considerable support to
the valid usage of these theoretical expressions to simulate dynamical
evolution in Fokker-Planck type calculations.
