"""
Landau damping initialisation function

[Wikipedia](https://en.wikipedia.org/wiki/Landau_damping)

```math
f(x,v) = \\frac{1}{\\sqrt{2\\pi}}(1+ ϵ \\cdot cos(kₓ x)) e^{-v^2/2}
```

"""
function landau( ϵ, kx, x, v )
    
    (1.0.+ϵ*cos.(kx*x))/sqrt(2π) .* transpose(exp.(-0.5*v.*v))
    
end

?landau