MATH-1255

Wrong usage of "Gaussian" function.

src/changes/changes.xml

@@ -54,6 +54,9 @@ If the output is not quite correct, check for invisible trailing spaces!
     </release>
 
     <release version="4.0" date="XXXX-XX-XX" description="">
+      <action dev="erans" type="fix" issue="MATH-1255">
+        Wrong neighbourhood size in class "KohonenUpdateAction" (package "o.a.c.m.ml.neuralnet.sofm").
+      </action>
       <action dev="psteitz" type="fix" issue="MATH-1252" due-to="John Bay"> <!-- backported to 3.6 -->
         ResizableDoubleArray constructor does not work with double array of size 1.
       </action>

src/main/java/org/apache/commons/math4/ml/neuralnet/sofm/KohonenUpdateAction.java

@@ -107,7 +107,7 @@ public class KohonenUpdateAction implements UpdateAction {
         final Gaussian neighbourhoodDecay
             = new Gaussian(currentLearning,
                            0,
-                           1d / currentNeighbourhood);
+                           currentNeighbourhood);
 
         if (currentNeighbourhood > 0) {
             // Initial set of neurons only contains the winning neuron.