Approximation of attractors of semidynamical systems

The problem of approximation with prescribed accuracy of the attractors of semidynamical systems is considered. The problem is formulated in terms of the function of the rate of attraction. New results on the structure of unstable manifolds in the neighbourhood of a non-hyperbolic point are used. For a certain class of maps the unstable manifold is effectively constructed and an estimate of the rate of attraction to it is found.