Although it is not possible, in general, to give a macro description of a micro model over the entire state space of the micro model, it is possible to aggregate exactly over a subspace. The set of micro states where aggregation is possible forms the aggregation set. The paper considers the...

(Approximation by Moving Equilibrium). The analysis of multivariate dynamical models can sometimes be considerably simplified by the assumption that one or several variables move infinitely fast to their equilibrium values. The method is known as the 'moving equilibrium method'. Various...