--- trunk/OOPSE/libmdtools/CutoffGroup.hpp	2004/05/12 15:02:03	1164
+++ trunk/OOPSE/libmdtools/CutoffGroup.hpp	2004/05/12 15:58:35	1166
@@ -3,68 +3,85 @@ class CutoffGroup{
 #include "Atom.hpp"
 
 class CutoffGroup{
-  public:
-
-    void addAtom(Atom* atom) {cutoffAtomList.push_back(atom);}
-
-    Atom* beginAtom(vector<Atom*>::iterator& i){
-      i = cutoffAtomList.begin();
-      return i != cutoffAtomList.end()? *i : NULL;
-    }
-
-    Atom* nextAtom(vector<Atom*>::iterator& i){
-      i++;
-      return i != cutoffAtomList.end()? *i : NULL;
-    }
-
-    double getMass(){
-      vector<Atom*>::iterator i;
-      Atom* atom;
-      double totalMass;
-      double mass;
+public:
+  
+  CutoffGroup() { 
+    haveTotalMass = false; 
+    totalMass = 0.0;
+  }
+  
+  void addAtom(Atom* atom) {cutoffAtomList.push_back(atom);}
+  
+  Atom* beginAtom(vector<Atom*>::iterator& i){
+    i = cutoffAtomList.begin();
+    return i != cutoffAtomList.end()? *i : NULL;
+  }
+  
+  Atom* nextAtom(vector<Atom*>::iterator& i){
+    i++;
+    return i != cutoffAtomList.end()? *i : NULL;
+  }
+  
+  double getMass(){
+    vector<Atom*>::iterator i;
+    Atom* atom;
+    double mass;
     
-      totalMass = 0;
+    if (!haveTotalMass) {
 
+      totalMass = 0;
+      
       for(atom = beginAtom(i); atom != NULL; atom = nextAtom(i)){
         mass = atom->getMass();
         totalMass += mass;
       }
 
-      return totalMass;
+      haveTotalMass = true;
     }
     
-    void getCOM(double com[3]){
-      vector<Atom*>::iterator i;
-      Atom* atom;
-      double pos[3];
-      double totalMass;
-      double mass;
-      
-      com[0] = 0;
-      com[1] = 0;
-      com[2] = 0;
-      totalMass = 0;
+    return totalMass;
+  }
+  
+  void getCOM(double com[3]){
 
+    vector<Atom*>::iterator i;
+    Atom* atom;
+    double pos[3];
+    double mass;
+    
+    com[0] = 0;
+    com[1] = 0;
+    com[2] = 0;
+    totalMass = getMass();    
+    
+    if (cutoffAtomList.size() == 1) {
+      
+      beginAtom(i)->getPos(com);
+      
+    } else {
+      
       for(atom = beginAtom(i); atom != NULL; atom = nextAtom(i)){
         mass = atom->getMass();
-        totalMass += mass;
         atom->getPos(pos);
         com[0] += pos[0] * mass;
         com[1] += pos[1] * mass;
         com[2] += pos[2] * mass;
       }
-
+      
       com[0] /= totalMass;
       com[1] /= totalMass;
       com[2] /= totalMass;
-           
     }
-      
-    int getNumAtom() {return cutoffAtomList.size();}
+    
+  }
+  
+  int getNumAtom() {return cutoffAtomList.size();}
+  
+private:
+  vector<Atom*> cutoffAtomList;
+  bool haveTotalMass;
+  double totalMass;
 
-  private:
-    vector<Atom*> cutoffAtomList;
-
 };
 
 #endif