Merge pull request rasmusbergpalm#24 from mohsenali/patch-1

Update nntrain.m

Author: rasmusbergpalm

NN/nntrain.m

@@ -12,7 +12,7 @@
     if nn.normalize_input==1
         [x, mu, sigma] = zscore(x);
         nn.normalizeMean = mu;
-        sigma(sigma==0) = 1;
+        sigma(sigma==0) = 0.0001;%this should be very small value. 
         nn.normalizeStd  = sigma;
     end