Fix a bug, add some testcases.

diff --git a/math_utils.py b/math_utils.py
index 28b8e6b3b6d9a407c6f263220e314d9d4acacbc0..f77e0a1f2514f5a0201c81f57e9740d36d2ede47 100644 (file)
--- a/math_utils.py
+++ b/math_utils.py
@@ -21,6 +21,10 @@ class RunningMedian(object):
     >>> median.add_number(5)
     >>> median.get_median()
     5
+    >>> median.get_mean()
+    5.2
+    >>> round(median.get_stdev(), 2)
+    6.99
     """
 
     def __init__(self):
@@ -57,6 +61,7 @@ class RunningMedian(object):
         mean = self.get_mean()
         variance = 0.0
         for n in self.lowers:
+            n = -n
             variance += (n - mean) ** 2
         for n in self.highers:
             variance += (n - mean) ** 2