[commons-statistics] branch master updated: LogisticsDistribution: Fix the variance computation

[aherbert]

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aherbert pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-statistics.git


The following commit(s) were added to refs/heads/master by this push:
     new 97d2396  LogisticsDistribution: Fix the variance computation
97d2396 is described below

commit 97d23965e8c8770b2b52263b3576681ece4c43a0
Author: aherbert <aherb...@apache.org>
AuthorDate: Wed Sep 11 17:10:26 2019 +0100

    LogisticsDistribution: Fix the variance computation
---
 .../commons/statistics/distribution/LogisticDistribution.java  |  2 +-
 .../statistics/distribution/LogisticsDistributionTest.java     | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git 
a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/LogisticDistribution.java
 
b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/LogisticDistribution.java
index ecf9efb..985e289 100644
--- 
a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/LogisticDistribution.java
+++ 
b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/LogisticDistribution.java
@@ -105,7 +105,7 @@ public class LogisticDistribution extends 
AbstractContinuousDistribution {
     /** {@inheritDoc} */
     @Override
     public double getVariance() {
-        return oneOverScale * oneOverScale * PI_SQUARED_OVER_THREE;
+        return scale * scale * PI_SQUARED_OVER_THREE;
     }
 
     /** {@inheritDoc} */
diff --git 
a/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/LogisticsDistributionTest.java
 
b/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/LogisticsDistributionTest.java
index 1aa6d0e..310d8d8 100644
--- 
a/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/LogisticsDistributionTest.java
+++ 
b/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/LogisticsDistributionTest.java
@@ -40,6 +40,16 @@ public class LogisticsDistributionTest extends 
ContinuousDistributionAbstractTes
         Assertions.assertTrue(d.isSupportConnected());
     }
 
+    @Test
+    public void testMeanAndVariance() {
+        LogisticDistribution d = makeDistribution();
+        // Constructor 'location' parameter = mean
+        Assertions.assertEquals(2.0, d.getMean());
+        // Variance = (s^2 * pi^2) / 3
+        // Constructor 'scale' parameter = s
+        Assertions.assertEquals(5 * 5 * Math.PI * Math.PI / 3, 
d.getVariance());
+    }
+
     @Override
     public LogisticDistribution makeDistribution() {
         return new LogisticDistribution(2, 5);