  Exploiting the coherent medium approximation, random walk among sites
distributed randomly in space is investigated when the jump rate depends on the
distance between two adjacent sites. In one dimension, it is shown that when
the jump rate decays exponentially in the long distance limit, a non-diffusive
to diffusive transition occurs as the density of sites is increased. In three
dimensions, the transition exists when the jump rate has a super Gaussian
decay.
