Chapter 10 Other Approaches

In this final chapter I want to mention briefly three other approaches to the general center-focus problem. In the first, we try to identify whole components of the center variety by finding their intersections with specific subsets of parameter space and then showing that the type of center is “rigid”. In the second approach, we try to see the consequences of a center on its bounding separatrix cycle. Monodromytype arguments play an implicit role in both of these approaches. The last section describes attempts to circumvent some of the computational complexity of the center focus problem by working over finite fields. It ends with an experimental approach to the center-focus via intensive computations using modular arithmetic and an application of the Weil conjectures. It makes a fitting conclusion to our range of monodromy techniques, since the arithmetic analog of monodromy was an essential ingredient in Deligne’s proof of the Weil conjectures [59].