If you have a dynamical system with zero eigenvalues in the linear part, one common method to restrict it to the center manifold is to transform it such that the linear terms are in Jordan normal form and then apply transformations of the form y=h(x,..) to isolate the center manifold. h can be assumed as a partial power series to get an easy approximate solution. This is easily applied if the dynamical system has polynomial form and there are many examples on the web.
But how do you apply this method if the system contains non-polynomial terms? Can we use a Taylor-expansion? Has anyone a good step-by-step example?