code: private void makeIncoming() {
          if (stays == null && move == null) {
              for (BitSet in : ins) {
                  in.clear();
              }
              stays = new BitSet();
              move = new BitSet();
              for (int i = 0; i < hosts.length; i++) {
                  if (hosts[i] != null && hosts[i].isInstantiated()) {
                      int newPos = hosts[i].getValue();
                      if (oldPos[i] != -1 && newPos != oldPos[i]) {
                          //The VM has move
                          ins[newPos].set(i);
                          move.set(i);
                      } else if (newPos == oldPos[i]) {
                          stays.set(i);
                      }
                  }
              }
          }
      }
docs: For each node, we fill ins to indicate the VMs
  that go on this node. We also fulfill stays and move
  TODO: stays and move seems redundant !