streamplot



using Makie

struct FitzhughNagumo{T}
    ϵ::T
    s::T
    γ::T
    β::T
end

P = FitzhughNagumo(0.1, 0.0, 1.5, 0.8)
f(x, P::FitzhughNagumo) = Point2f0(
    (x[1]-x[2]-x[1]^3+P.s)/P.ϵ,
    P.γ*x[1]-x[2] + P.β
)
f(x) = f(x, P)
streamplot(f, -1.5..1.5, -1.5..1.5, colormap = :magma)