ActsTrk::IHGTDClusteringTool::Cluster Node1 ActsTrk::IHGTDClustering Tool::Cluster     Node2 std::vector< Identifier ::value_type > + elements   Node2->Node1 +ids Node3 std::vector< int > + elements + elements   Node3->Node1 +tots Node4 std::vector< double > + elements + elements   Node4->Node1 +times