Simple chaotic maps are used to illustrate the inherent instability of
trajectory solutions to the Frobenius-Perron equation. This is demons
trated by the difference in the behavior of delta-function solutions a
nd of extended densities. Extended densities evolve asymptotically and
irreversibly into invariant measures on stationary attractors. Pointw
ise trajectories chaotically roam over these attractors forever. Perio
dic Gaussian distributions on the unit interval are used to provide in
sight. Viewing evolving densities as ensembles of unstable pointwise t
rajectories gives densities a stochastic interpretation. (C) 1995 Amer
ican Institute of Physics.