Oscillating FHN systems

    du/dt = F(u, v) = u(1 - u)(u - a) - v,
    dv/dt = H(u, v) = ε (bu - v).

For negative a values the (u=0, v=0) fixed point is unstable and u, v oscillate.
a b ε

dt u0 v0 Ymin Ymax field
The script makes 800 time steps dt.
Heart rhythms     updated 24 Dec 2011