Fig. 6

Two-parameter bifurcation diagram of the fast system of Equations 4a-4c in the $(z,s)$-plane. The loci of Hopf H (red curve) and homoclinic HC (blue curve) bifurcations emerge from the Bogdanov-Takens point BT at $(z,s)\simeq (0.004985,-1.599)$. The curve H is plotted as a solid/dashed line when the Hopf bifurcation is supercritical/subcritical. The saddle-node of periodic orbits SNp (purple curve) exists between the Bautin bifurcation point B at $(z,s)\simeq (-0.004541,-1.75)$ and the SNpHC at $(z,s)\simeq (0.006291,-2.339)$.