Hi, I want to generate a local spanning tree of one graph(not MST) so I construct a subgraph of the original graph by add_vertex() and add_edge() function. The problem is that after the add_vertex(). the local tree generate edges between the vertexes automaticlly. If I call add_edge() again, it will dumplicat edges since all the edges between existing vertex have been added by add_vertex() function. I checked the example code of how to add vertex and edge in subgraph. It seems the add_vertex() function should not add edges automaticlly. SUBGRAPH m_g; ... //Create spanning tree SUBGRAPH& localTree = m_g.create_subgraph(); //Add one vertex as root in spanning tree boost::add_vertex(m_root, localTree); //Add descendants to the tree typedef graph_traits<SUBGRAPH> GTraits; GTraits::out_edge_iterator tmpei, tmpei_end; std::pair<GTraits::out_edge_iterator, GTraits::out_edge_iterator> p; p = out_edges(m_root, m_g); tmpei = p.first; tmpei_end = p.second; while ( tmpei != tmpei_end ) { //Descendant PolyGraphVertex tmpv = target(*tmpei , m_g); //Add descendant boost::add_vertex(tmpv, localTree); //Add an edge from ancestor to descendant boost::add_edge(m_root,tmpv,localTree); tmpei++; }