Global phase portraits of the key pitchfork bifurcation

Abstract

This paper deals with the following quadratic polynomial differential system$\frac{dx}{dt}=y^{2}-y-x,$ $\frac{dy}{dt}=x^{2}$ $-\,~\mu~x-y,$with parameter $\mu\in\mathbb{R}$, which is the key example for studying the pitchfork bifurcation of a singular point. We classify the global phase portraits in the Poincare disc of this system when $\mu$ varies.