Recently, geometric singular perturbation theory has been extended considerably while at the same time producing many new applications. We will review a number of aspects relevant to non-linear dynamics to apply this to periodic solutions within slow manifolds and to review a number of non-hyperbolic cases. The results are illustrated by examples.Keywords Singular perturbations . Slow manifolds . Periodic solutions . Nonhyperbolic This paper deals with slow-fast initial value problems that are of the forṁAs usual, ε is a small positive parameter, and an overdot denotes differentiation with respect to time. For a number of results, the vector fields f and g explicitly depending on time t present no obstruction. Part of the paper is a tutorial, but there are some new results.
The Tikhonov theoremIn singular perturbations, certain attraction (or hyperbolicity) properties of the regular (outer) expansion play an essential part in the construction of the formal approximation. Remarkably enough, this hyperbolicity does not include the behaviour of the slow equation.In the constructions, the following theorem provides a basic boundary layer property of the solution. Theorem 1.1. (Tikhonov, 1952, see [15]) Consider the initial value probleṁ
For f and g, we take sufficiently smooth vector functions in x, y and t; the dots represent (smooth) higherorder terms in ε.a. We assume that a unique solution of the initial value problem exists and suppose this holds also for the reduced probleṁ x = f (x, y, t), x(0) = x 0 ,
= g(x, y, t), with solutionsx(t),ȳ(t).Springer