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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);