def cubic_rbf(r, kappa):
    """
    Computes the Cubic Radial Basis Function between two points with distance `r`.

    Parameters
    ----------
    r : float
        Distance between point `x1` and `x2`.
    kappa : float
        Shape parameter.

    Returns
    -------
    phi : float
        Radial basis function response.
    """

    return (r * kappa) ** 3.