def foundation_profile(x, delta_f, L_o):
    """Return the idealised imperfection profile [m] - JIP.

    :param float x: Distance along profile [m]
    :param float delta_f: Imperfection height [m]
    :param float L_o: Natural wavelength [m]
    """
    return delta_f * (x / L_o) ** 3 * (4 - 3 * x / L_o)