[commons-rng] 01/02: UnitSphereSamplerTest: Test to show any normSq value after 0 is valid.

[aherbert]

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aherbert pushed a commit to branch master
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commit 52858ebe5277184a46c2d7fecfe55ea907d3c2ea
Author: Alex Herbert <aherb...@apache.org>
AuthorDate: Sun Mar 3 16:22:20 2019 +0000

    UnitSphereSamplerTest: Test to show any normSq value after 0 is valid.
---
 .../commons/rng/sampling/UnitSphereSamplerTest.java       | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git 
a/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/UnitSphereSamplerTest.java
 
b/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/UnitSphereSamplerTest.java
index 5d32105..0d64d26 100644
--- 
a/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/UnitSphereSamplerTest.java
+++ 
b/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/UnitSphereSamplerTest.java
@@ -96,6 +96,21 @@ public class UnitSphereSamplerTest {
     }
 
     /**
+     * Test to demonstrate that using floating-point equality of the norm 
squared with
+     * zero is valid. Any norm squared after zero should produce a valid 
scaling factor.
+     */
+    @Test
+    public void testNextNormSquaredAfterZeroIsValid() {
+        // The sampler explicitly handles length == 0 using recursion.
+        // Anything above zero should be valid.
+        final double normSq = Math.nextAfter(0, 1);
+        // Map to the scaling factor
+        final double f = 1 / Math.sqrt(normSq);
+        // As long as this is finite positive then the sampler is valid
+        Assert.assertTrue(f > 0 && f <= Double.MAX_VALUE);
+    }
+
+    /**
      * @return the length (L2-norm) of given vector.
      */
     private static double length(double[] vector) {