  Motivated by the problem of thermalization in heavy-ion collisions, we
present numerical simulations of the nonequilibrium evolution of the O(N) model
in 1+2 dimensions with longitudinal expansion and in the presence of a
background field. We work in the NLO approximation of the 1/N expansion and
consider both the strong and weak coupling cases. Special emphasis is put on
the difference between the 2PI formalism and the classical statistical
approach. In the 2PI case at strong coupling, we find some evidence of the
Bose-Einstein (exponential) distribution in the expanding system.
