From 2f457f0a18a8bc5fc82e23f9436b732474947da9 Mon Sep 17 00:00:00 2001
From: cmsbuild <cmsbuild@cern.ch>
Date: Fri, 23 Jan 2015 21:37:21 +0100
Subject: [PATCH] Merge pull request #7348 from bendavid/hepmcweightfix

Fix handling of weights in generator interfaces
---
 GeneratorInterface/Core/interface/HadronizerFilter.h   |  6 ++----
 .../Pythia8Interface/plugins/Pythia8Hadronizer.cc      | 10 +++++++---
 .../GeneratorProducts/interface/GenEventInfoProduct.h  |  6 +++++-
 .../GeneratorProducts/src/GenEventInfoProduct.cc       |  2 +-
 4 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/GeneratorInterface/Core/interface/HadronizerFilter.h b/GeneratorInterface/Core/interface/HadronizerFilter.h
index 0da94ec3d6e43..f36b8b354fb70 100644
--- a/GeneratorInterface/Core/interface/HadronizerFilter.h
+++ b/GeneratorInterface/Core/interface/HadronizerFilter.h
@@ -224,12 +224,10 @@ namespace edm
       double multihadweight = double(naccept)/double(nAttempts_);
       
       //adjust weight for GenEventInfoProduct
-      std::vector<double> genEventInfoWeights = finalGenEventInfo->weights();
-      genEventInfoWeights.push_back(multihadweight);
-      finalGenEventInfo->setWeights(genEventInfoWeights);
+      finalGenEventInfo->weights()[0] *= multihadweight;
       
       //adjust weight for HepMC GenEvent (used e.g for RIVET)
-      finalEvent->weights().push_back(multihadweight);
+      finalEvent->weights()[0] *= multihadweight;
     }
     
     
diff --git a/GeneratorInterface/Pythia8Interface/plugins/Pythia8Hadronizer.cc b/GeneratorInterface/Pythia8Interface/plugins/Pythia8Hadronizer.cc
index e04b8d9b7ba6b..535d644dbf42d 100644
--- a/GeneratorInterface/Pythia8Interface/plugins/Pythia8Hadronizer.cc
+++ b/GeneratorInterface/Pythia8Interface/plugins/Pythia8Hadronizer.cc
@@ -484,7 +484,11 @@ bool Pythia8Hadronizer::hadronize()
 
   bool py8next = fMasterGen->next();
 
-  double mergeweight = fMasterGen.get()->info.mergingWeight();
+  double mergeweight = fMasterGen.get()->info.mergingWeightNLO();
+  if (fMergingHook) {
+    mergeweight *= fMergingHook->getNormFactor();
+  }
+  
   
   //protect against 0-weight from ckkw or similar
   if (!py8next || std::abs(mergeweight)==0.)
@@ -516,9 +520,9 @@ bool Pythia8Hadronizer::hadronize()
     return false;
   }
   
-  //add ckkw merging weight
+  //add ckkw/umeps/unlops merging weight
   if (mergeweight!=1.) {
-    event()->weights().push_back(mergeweight);
+    event()->weights()[0] *= mergeweight;
   }
   
   if (fEmissionVetoHook) {
diff --git a/SimDataFormats/GeneratorProducts/interface/GenEventInfoProduct.h b/SimDataFormats/GeneratorProducts/interface/GenEventInfoProduct.h
index 9196a47d99357..2525784bde5c9 100644
--- a/SimDataFormats/GeneratorProducts/interface/GenEventInfoProduct.h
+++ b/SimDataFormats/GeneratorProducts/interface/GenEventInfoProduct.h
@@ -25,8 +25,12 @@ class GenEventInfoProduct {
 
 	// getters
 
+	std::vector<double> &weights() { return weights_; }
 	const std::vector<double> &weights() const { return weights_; }
-	double weight() const;
+	
+	double weight() const { return weights_.empty() ? 1.0 : weights_[0]; }
+	
+	double weightProduct() const;
 
 	unsigned int signalProcessID() const { return signalProcessID_; }
 
diff --git a/SimDataFormats/GeneratorProducts/src/GenEventInfoProduct.cc b/SimDataFormats/GeneratorProducts/src/GenEventInfoProduct.cc
index b77136b3311be..570f29064c9c1 100644
--- a/SimDataFormats/GeneratorProducts/src/GenEventInfoProduct.cc
+++ b/SimDataFormats/GeneratorProducts/src/GenEventInfoProduct.cc
@@ -74,7 +74,7 @@ GenEventInfoProduct &GenEventInfoProduct::operator = (GenEventInfoProduct const
 	return *this;
 }
 
-double GenEventInfoProduct::weight() const
+double GenEventInfoProduct::weightProduct() const
 {
 	return std::accumulate(weights_.begin(), weights_.end(),
 	                       1., std::multiplies<double>());