models.py 文件源码

def matern(h, a, C0, s, b=0):
    """
    The Matérn model.

    For Matérn function see:
    Minasny, B., & McBratney, A. B. (2005). The Matérn function as a general model for soil variograms.
        Geoderma, 128(3–4 SPEC. ISS.), 192–207. http://doi.org/10.1016/j.geoderma.2005.04.003.

    :param h:   lag
    :param a:   range
    :param C0:  sill
    :param s:   smoothness parameter
    :param b:   nugget
    :return:
    """
    # prepare parameters
    r = a
    C0 -= b

    return b + C0 * (1 - ( (1 / (np.power(2, s - 1) * special.gamma(s))) * np.power(h / r, s) * special.kv(s, h / r) ))


# --- Adaptions using no nugget effect --- #