From 0e979cbf2e8ec1a8b0028a687d5dd1bf172245c5 Mon Sep 17 00:00:00 2001
From: Andrew McCluskey <andrew.mccluskey@diamond.ac.uk>
Date: Sat, 2 May 2020 11:04:57 +0100
Subject: [PATCH] add variance to distribution

---
 uravu/distribution.py            | 23 +++++++++++++++++++++--
 uravu/tests/test_distribution.py |  8 ++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/uravu/distribution.py b/uravu/distribution.py
index 7be95b5..0597f1a 100644
--- a/uravu/distribution.py
+++ b/uravu/distribution.py
@@ -90,15 +90,34 @@ def n(self):
         return np.percentile(self.samples, [50])[0]
 
     @property
-    def s(self):
+    def s(self, ddof=1):
         """
         Get the standard deviation of the distribution. For a non-normal distribution, this will return :py:attr:`None`.
 
+        Args:
+            ddof (:py:attr:`int`): Degrees of freedom to be included in calculation.
+
+        Returns:
+            :py:attr:`float` or :py:attr:`None`: Standard deviation of the distribution.
+        """
+        if self.normal:
+            return np.std(self.samples, ddof=ddof)
+        else:
+            return None
+
+    @property
+    def v(self, ddof=1):
+        """
+        Get the variance of the distribution. For a non-normal distribution, this will return :py:attr:`None`.
+
+        Args:
+            ddof (:py:attr:`int`): Degrees of freedom to be included in calculation.
+
         Returns:
             :py:attr:`float` or :py:attr:`None`: Standard deviation of the distribution.
         """
         if self.normal:
-            return np.std(self.samples)
+            return np.var(self.samples, ddof=ddof)
         else:
             return None
 
diff --git a/uravu/tests/test_distribution.py b/uravu/tests/test_distribution.py
index fafaaa3..6c4b414 100644
--- a/uravu/tests/test_distribution.py
+++ b/uravu/tests/test_distribution.py
@@ -109,6 +109,14 @@ def test_check_normality_less_than_3(self):
         distro = Distribution(np.random.randn(2))
         assert_equal(distro.normal, False)
 
+    def test_s(self):
+        """
+        Test the standard deviation and variance
+        """
+        distro = Distribution(np.random.randn(10000) * 10)
+        assert_almost_equal(distro.s, 10., decimal=1)
+        assert_almost_equal(distro.v, 100., decimal=0)
+
     def test_add_samples_single(self):
         """
         Test add_samples with a single value.