Repository: mmaelicke/scikit-gstat

Issue:
Scale of Dowd's estimator
Hey @mmaelicke,

Hope all is well, it's been a while!
I use a lot robust estimators through my work, and noticed that Dowd's is not scaled the same as others: it returns 2gamma instead of gamma, and so will have twice the values of e.g. Matheron's for the same data. We can see it in the doc: 
https://scikit-gstat.readthedocs.io/en/latest/_images/compare_estimators.png

Easy fix dividing by 2 here: https://github.com/mmaelicke/scikit-gstat/blob/81463bbadec56e892135122856613b57ed25bea7/skgstat/estimators.py#L178
I'll open a PR!

Discussion:

Patch:
diff --git a/skgstat/estimators.py b/skgstat/estimators.py
index 74cf62c..adb4dd1 100644
--- a/skgstat/estimators.py
+++ b/skgstat/estimators.py
@@ -175,7 +175,7 @@ def dowd(x):
 
     """
     # convert
-    return 2.198 * np.nanmedian(x)**2
+    return 2.198 * np.nanmedian(x)**2 / 2
 
 
 @jit(forceobj=True)


Test patch:
diff --git a/skgstat/tests/test_estimator.py b/skgstat/tests/test_estimator.py
index 548948a..320191f 100644
--- a/skgstat/tests/test_estimator.py
+++ b/skgstat/tests/test_estimator.py
@@ -55,8 +55,8 @@ class TestEstimator(unittest.TestCase):
         x2 = np.random.gamma(10, 4, 100)
 
         # test
-        self.assertAlmostEqual(dowd(x1), 2.0873, places=4)
-        self.assertAlmostEqual(dowd(x2), 3170.97, places=2)
+        self.assertAlmostEqual(dowd(x1), 1.0437, places=4)
+        self.assertAlmostEqual(dowd(x2), 1585.48, places=2)
 
     def test_genton(self):
         # extract actual estimator