code: int newEdge_(int origin_vertex) {
  		int edge = m_edges.newElement();
  		int edgeVertices = m_edge_vertices.createList();
  		setEdgeOriginVertices_(edge, edgeVertices);
  		if (origin_vertex != -1)
  			m_edge_vertices.addElement(edgeVertices, origin_vertex);
  
  		return edge;
  	}
docs: Creates a new unattached edge with the given origin.