The Poincaré center problem

We present two examples of real planar polynomial vector fields with an orbitally linearizable saddle point such that they are neither rationally reversible nor Liouvillian integrable. We show that vector fields from one of these examples form an isolated component of the so-called integrable saddle variety. Next, we discuss the problem of partial duality between real centers and real integrable saddles and the problem of continuous moduli for the center variety. © Springer Science+Business Media, LLC 2008.