Fig. 9.

Snapshots of the moving phase-plane diagram for the linear system (29)–(30) for $\alpha =1$, $ϵ=0.1$, $f=48$ and representative values of t within one cycle ($T=1000$). The solid-red lines represent the moving v-nullcline. The dashed-red lines represent the v-nullclines for $A_t=0$ (middle), $A_t=1$ (top), and $A_t=-1$ (bottom). The solid-green line represents the (fixed) w-nullcline. The fixed solid-red line and the solid-green line represent the v- and w-nullclines for the unforced system ($A_t=0$), respectively. The dashed-red lines represent the v-nullclines for $A_t=1$ (above), $A_t=0$ (middle), and $A_t=-1$ (below). As t increases, the red nullcline moves cyclically between the two dashed-red lines. The blue dot indicates the initial location of the trajectory ($t=0=1000$)