Merge pull request #122 from GeoStat-Framework/add_cubic_model

Add Cubic covariance model
GeoStat-Framework · Dec 9, 2020 · 473ce01 · 473ce01
2 parents b56a1b3 + d9cd3d0
commit 473ce01
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diff --git a/examples/02_cov_model/README.rst b/examples/02_cov_model/README.rst
@@ -64,6 +64,7 @@ The following standard covariance models are provided by GSTools
     Matern
     Stable
     Rational
+    Cubic
     Linear
     Circular
     Spherical

diff --git a/gstools/__init__.py b/gstools/__init__.py
@@ -55,8 +55,9 @@
    Gaussian
    Exponential
    Matern
-   Rational
    Stable
+   Rational
+   Cubic
    Linear
    Circular
    Spherical
@@ -127,8 +128,9 @@
     Gaussian,
     Exponential,
     Matern,
-    Rational,
     Stable,
+    Rational,
+    Cubic,
     Linear,
     Circular,
     Spherical,
@@ -155,8 +157,9 @@
     "Gaussian",
     "Exponential",
     "Matern",
-    "Rational",
     "Stable",
+    "Rational",
+    "Cubic",
     "Linear",
     "Circular",
     "Spherical",

diff --git a/gstools/covmodel/__init__.py b/gstools/covmodel/__init__.py
@@ -29,8 +29,9 @@
    Gaussian
    Exponential
    Matern
-   Rational
    Stable
+   Rational
+   Cubic
    Linear
    Circular
    Spherical
@@ -54,8 +55,9 @@
     Gaussian,
     Exponential,
     Matern,
-    Rational,
     Stable,
+    Rational,
+    Cubic,
     Linear,
     Circular,
     Spherical,
@@ -75,8 +77,9 @@
     "Gaussian",
     "Exponential",
     "Matern",
-    "Rational",
     "Stable",
+    "Rational",
+    "Cubic",
     "Linear",
     "Circular",
     "Spherical",

diff --git a/gstools/covmodel/models.py b/gstools/covmodel/models.py
@@ -12,6 +12,7 @@
    Matern
    Stable
    Rational
+   Cubic
    Linear
    Circular
    Spherical
@@ -33,6 +34,7 @@
     "Matern",
     "Stable",
     "Rational",
+    "Cubic",
     "Linear",
     "Circular",
     "Spherical",
@@ -433,6 +435,36 @@ def calc_integral_scale(self):  # noqa: D102
         )
 
 
+class Cubic(CovModel):
+    r"""The Cubic covariance model.
+
+    A model with reverse curvature near the origin and a finite range of
+    correlation.
+
+    Notes
+    -----
+    This model is given by the following correlation function:
+
+    .. math::
+       \rho(r) =
+       \begin{cases}
+       1- 7 \left(s\cdot\frac{r}{\ell}\right)^{2}
+       + \frac{35}{4} \left(s\cdot\frac{r}{\ell}\right)^{3}
+       - \frac{7}{2} \left(s\cdot\frac{r}{\ell}\right)^{5}
+       + \frac{3}{4} \left(s\cdot\frac{r}{\ell}\right)^{7}
+       & r<\frac{\ell}{s}\\
+       0 & r\geq\frac{\ell}{s}
+       \end{cases}
+
+    Where the standard rescale factor is :math:`s=1`.
+    """
+
+    def cor(self, h):
+        """Spherical normalized correlation function."""
+        h = np.minimum(np.abs(h, dtype=np.double), 1.0)
+        return 1.0 - 7 * h ** 2 + 8.75 * h ** 3 - 3.5 * h ** 5 + 0.75 * h ** 7
+
+
 class Linear(CovModel):
     r"""The bounded linear covariance model.
 

diff --git a/tests/test_covmodel.py b/tests/test_covmodel.py
@@ -13,8 +13,9 @@
     CovModel,
     Gaussian,
     Exponential,
-    Rational,
     Stable,
+    Rational,
+    Cubic,
     Matern,
     Linear,
     Circular,
@@ -68,8 +69,9 @@ def setUp(self):
         self.std_cov_models = [
             Gaussian,
             Exponential,
-            Rational,
             Stable,
+            Rational,
+            Cubic,
             Matern,
             Linear,
             Circular,
-Original file line number
+Diff line change
@@ Expand Up @@
         Matern
         Stable
         Rational
+        Cubic
         Linear
         Circular
         Spherical
@@ Expand Down @@