diff --git a/som.cabal b/som.cabal
--- a/som.cabal
+++ b/som.cabal
@@ -1,5 +1,5 @@
 name:           som
-version:        7.2.1
+version:        7.2.2
 synopsis:       Self-Organising Maps
 description:    A Kohonen Self-organising Map (SOM) maps input patterns 
                 onto a regular grid (usually two-dimensional) where each
diff --git a/src/Data/Datamining/Clustering/SOMInternal.hs b/src/Data/Datamining/Clustering/SOMInternal.hs
--- a/src/Data/Datamining/Clustering/SOMInternal.hs
+++ b/src/Data/Datamining/Clustering/SOMInternal.hs
@@ -64,7 +64,7 @@
 instance (Floating a, Fractional a, Num a)
     => LearningFunction (DecayingGaussian a) where
   type LearningRate (DecayingGaussian a) = a
-  rate (DecayingGaussian r0 rf w0 wf tf) t d = r * exp (-(d*d)/(w*w))
+  rate (DecayingGaussian r0 rf w0 wf tf) t d = r * exp (-(d*d)/(2*w*w))
     where a = t/tf
           r = r0 * ((rf/r0)**a)
           w = w0 * ((wf/w0)**a)