There are many versions for the ``van der Pol’’ equation. Among them, there is this one, involving the cubic term, which reads
and which was investigated in details in . This is sstem is a semi-conservative system which means that there is a continuum of attractors, that is, many many different attractors co-exist in the state space . When parameter values are , , and , and initial conditions are
there is a toroidal chaotic attractor as shown in Fig. 1.
 C. Letellier, V. Messager & R. Gilmore, From quasi-periodicity to toroidal chaos : analogy between the Curry-Yorke map and the van der Pol system, Physical Review E, 77 (4), 046203, 2008.
 O. Ménard, C. Letellier, J. Maquet, L. Le Sceller & G. Gouesbet, Analysis of a non synchronized sinusoidally driven dynamical system, International Journal of Bifurcation & Chaos, 10 (7), 1759-1772, 2000.