Qualitative analysis of the phase portrait for a class of planar vector fields via the comparison method Original Research Article

The phase portrait of the second-order differential equation View the MathML sourceẍ+∑l=0nfl(x)ẋl=0, Turn MathJax on is studied. Some results concerning existence, non-existence and uniqueness of limit cycles are presented. In particular, a generalization of the classical Massera uniqueness result is proved.