bug fix for stochastic collocation

mluq/src/estimators/datastructure/WelfordAggregate.hpp

@@ -83,8 +83,13 @@ struct Mean {
 
   void UpdateParallel(SampleCounter ctr, Weights wgt, int commSplit) {
     C = abs(PPM->SumAcrossComm(ctr.Mcomm * Ccomm, commSplit) / ctr.M);
-    Q = abs(PPM->SumAcrossComm(wgt.Wcomm * Qcomm, commSplit) / wgt.W);
-    Y = abs(PPM->SumAcrossComm(wgt.Wcomm * Ycomm, commSplit) / wgt.W);
+    if (wgt.W == ctr.M) {  // Monte Carlo Case
+      Q = abs(PPM->SumAcrossComm(ctr.Mcomm * Qcomm, commSplit) / ctr.M);
+      Y = abs(PPM->SumAcrossComm(ctr.Mcomm * Ycomm, commSplit) / ctr.M);
+    } else {  // Stochastic Collocation Case
+      Q = abs(PPM->SumAcrossComm(wgt.Wcomm * Qcomm, commSplit));
+      Y = abs(PPM->SumAcrossComm(wgt.Wcomm * Ycomm, commSplit));
+    }
   }
 
   friend Logging &operator<<(Logging &s, const Mean &mean) {