@Override
 public M createInitialMessage() {
   return typeOps.createZero();
 }
 @Override
 public void combine(WritableComparable vertexIndex, M originalMessage, M messageToCombine) {
   if (originalMessage.compareTo(messageToCombine) < 0) {
     typeOps.set(originalMessage, messageToCombine);
   }
 }