  A soliton cellular automaton associated with crystals of symmetric tensor
representations of the quantum affine algebra U'_q(A^{(1)}_M) is introduced. It
is a crystal theoretic formulation of the generalized box-ball system in which
capacities of boxes and carriers are arbitrary and inhomogeneous. Scattering
matrices of two solitons coincide with the combinatorial R matrices of
U'_q(A^{(1)}_{M-1}). A piecewise linear evolution equation of the automaton is
identified with an ultradiscrete limit of the nonautonomous discrete KP
equation. A class of N soliton solutions is obtained through the
ultradiscretization of soliton solutions of the latter.
