How to use the pykrige.variogram_models.linear_variogram_model function in PyKrige

def test_core_calculate_variogram_model():

    res = core._calculate_variogram_model(
        np.array([1.0, 2.0, 3.0, 4.0]),
        np.array([2.05, 2.95, 4.05, 4.95]),
        "linear",
        variogram_models.linear_variogram_model,
        False,
    )
    assert_allclose(res, np.array([0.98, 1.05]), 0.01, 0.01)

    res = core._calculate_variogram_model(
        np.array([1.0, 2.0, 3.0, 4.0]),
        np.array([2.05, 2.95, 4.05, 4.95]),
        "linear",
        variogram_models.linear_variogram_model,
        True,
    )
    assert_allclose(res, np.array([0.98, 1.05]), 0.01, 0.01)

    res = core._calculate_variogram_model(
        np.array([1.0, 2.0, 3.0, 4.0]),
        np.array([1.0, 2.8284271, 5.1961524, 8.0]),

z, ss = core._krige(
        np.vstack((data[:, 0], data[:, 1])).T,
        data[:, 2],
        np.array([18.8, 67.9]),
        variogram_models.linear_variogram_model,
        [0.006, 0.1],
        "euclidean",
    )
    assert z == approx(1.6364, rel=1e-4)
    assert ss == approx(0.4201, rel=1e-4)

    z, ss = core._krige(
        np.vstack((data[:, 0], data[:, 1])).T,
        data[:, 2],
        np.array([43.8, 24.6]),
        variogram_models.linear_variogram_model,
        [0.006, 0.1],
        "euclidean",
    )
    assert z == approx(2.822, rel=1e-3)
    assert ss == approx(0.0, rel=1e-3)

One of 'euclidean' or 'geographic'. Determines if the x and y
        coordinates are interpreted as on a plane ('euclidean') or as
        coordinates on a sphere ('geographic'). In case of geographic
        coordinates, x is interpreted as longitude and y as latitude
        coordinates, both given in degree. Longitudes are expected in
        [0, 360] and latitudes in [-90, 90]. Default is 'euclidean'.

    References
    ----------
    .. [1] P.K. Kitanidis, Introduction to Geostatistcs: Applications in
       Hydrogeology, (Cambridge University Press, 1997) 272 p.
    """

    eps = 1.0e-10  # Cutoff for comparison to zero
    variogram_dict = {
        "linear": variogram_models.linear_variogram_model,
        "power": variogram_models.power_variogram_model,
        "gaussian": variogram_models.gaussian_variogram_model,
        "spherical": variogram_models.spherical_variogram_model,
        "exponential": variogram_models.exponential_variogram_model,
        "hole-effect": variogram_models.hole_effect_variogram_model,
    }

    def __init__(
        self,
        x,
        y,
        z,
        variogram_model="linear",
        variogram_parameters=None,
        variogram_function=None,
        nlags=6,

Enables program text output to monitor kriging process.
        Default is False (off).
    enable_plotting : boolean, optional
        Enables plotting to display variogram. Default is False (off).

    References
    ----------
    .. [1] P.K. Kitanidis, Introduction to Geostatistcs: Applications in
       Hydrogeology, (Cambridge University Press, 1997) 272 p.
    """

    UNBIAS = True  # This can be changed to remove the unbiasedness condition
    # Really for testing purposes only...
    eps = 1.0e-10  # Cutoff for comparison to zero
    variogram_dict = {
        "linear": variogram_models.linear_variogram_model,
        "power": variogram_models.power_variogram_model,
        "gaussian": variogram_models.gaussian_variogram_model,
        "spherical": variogram_models.spherical_variogram_model,
        "exponential": variogram_models.exponential_variogram_model,
        "hole-effect": variogram_models.hole_effect_variogram_model,
    }

    def __init__(
        self,
        x,
        y,
        z,
        val,
        variogram_model="linear",
        variogram_parameters=None,
        variogram_function=None,

Scaling is applied after rotation.
    verbose : bool, optional
        Enables program text output to monitor kriging process.
        Default is False (off).
    enable_plotting : bool, optional
        Enables plotting to display variogram. Default is False (off).

    References
    ----------
    .. [1] P.K. Kitanidis, Introduction to Geostatistcs: Applications in
       Hydrogeology, (Cambridge University Press, 1997) 272 p.
    """

    eps = 1.0e-10  # Cutoff for comparison to zero
    variogram_dict = {
        "linear": variogram_models.linear_variogram_model,
        "power": variogram_models.power_variogram_model,
        "gaussian": variogram_models.gaussian_variogram_model,
        "spherical": variogram_models.spherical_variogram_model,
        "exponential": variogram_models.exponential_variogram_model,
        "hole-effect": variogram_models.hole_effect_variogram_model,
    }

    def __init__(
        self,
        x,
        y,
        z,
        val,
        variogram_model="linear",
        variogram_parameters=None,
        variogram_function=None,

Enables program text output to monitor kriging process.
        Default is False (off).
    enable_plotting : boolean, optional
        Enables plotting to display variogram. Default is False (off).

    References
    ----------
    .. [1] P.K. Kitanidis, Introduction to Geostatistcs: Applications in
       Hydrogeology, (Cambridge University Press, 1997) 272 p.
    """

    UNBIAS = True  # This can be changed to remove the unbiasedness condition
    # Really for testing purposes only...
    eps = 1.0e-10  # Cutoff for comparison to zero
    variogram_dict = {
        "linear": variogram_models.linear_variogram_model,
        "power": variogram_models.power_variogram_model,
        "gaussian": variogram_models.gaussian_variogram_model,
        "spherical": variogram_models.spherical_variogram_model,
        "exponential": variogram_models.exponential_variogram_model,
        "hole-effect": variogram_models.hole_effect_variogram_model,
    }

    def __init__(
        self,
        x,
        y,
        z,
        variogram_model="linear",
        variogram_parameters=None,
        variogram_function=None,
        nlags=6,