--- trunk/gadget/popinfo.h	2014/02/10 17:09:07	1
+++ trunk/gadget/popinfo.h	2015/04/29 12:55:30	2
@@ -2,6 +2,7 @@
 #define popinfo_h
 
 #include "gadget.h"
+#include "mathfunc.h"
 
 /**
  * \class PopInfo
@@ -48,7 +49,24 @@
    * \brief This operator will add an existing PopInfo to the current PopInfo
    * \param a is the PopInfo to add
    */
-  PopInfo& operator += (const PopInfo& a);
+  PopInfo& operator += (const PopInfo& a){
+	  if (isZero(N + a.N)) {
+	    W = 0.0;
+	    N = 0.0;
+	  } else if (isZero(a.N)) {
+	    //adding a zero popinfo, so don't do anything
+	  } else if (isZero(N)) {
+	    W = a.W;
+	    N = a.N;
+	  } else {
+	    W = (N * W + a.N * a.W) / (N + a.N);
+	    N = N + a.N;
+	  }
+	  return *this;
+	}
+
+
+						  ;
   /**
    * \brief This operator will multiply the PopInfo by a constant
    * \param a is the constant