Function numeric_diffusion_dx 

pub fn numeric_diffusion_dx<P: StochasticProcess1D + ?Sized>(
    p: &P,
    t: f64,
    x: f64,
) -> f64

Central finite difference of the diffusion coefficient in the state — the default for StochasticProcess1D::diffusion_dx, callable from implementations that override it for one branch of their dynamics.