Critical Periods of Planar Revertible Vector Field with Third-Degree Polynomial Functions.

Pei Yu Maoan Han Critical Periods of Planar Revertible Vector Field with Third-Degree Polynomial Functions. 419-433 2009 19 I. J. Bifurcation and Chaos 1 http://dx.doi.org/10.1142/S0218127409022981 db/journals/ijbc/ijbc19.html#YuH09