  We investigate a 3-phase deterministic one-dimensional phase ordering model
in which interfaces move ballistically and annihilate upon colliding. We
determine analytically the autocorrelation function A(t). This is done by
computing generalized first-passage type probabilities P_n(t) which measure the
fraction of space crossed by exactly n interfaces during the time interval
(0,t), and then expressing the autocorrelation function via P_n's. We further
reveal the spatial structure of the system by analyzing the domain size
distribution.
