def rk4(ode,y,t,h):

    """
    ode ... ordinary differential equation to solve
    y   ... A vector fucntion containing D and dD/dt
    t   ... time to integrate over
    h   ... integration step

    Method using here is the classic Runge-Kutta (4-th order), acquired L10.

    """

    k1 = h * ode(t, y)
    k2 = h * ode(t+h/2., y+k1/2.)
    k3 = h * ode(t+h/2., y+k2/2.)
    k4 = h * ode(t+h, y+k3)

    return k1/6. + k2/3. + k3/3. + k4/6.