Edge edge45=graphModel.factory().newEdge(node4, node5, false);
Edge edge51=graphModel.factory().newEdge(node5, node1, false);
Edge edge16=graphModel.factory().newEdge(node1, node6, false);
Edge edge67=graphModel.factory().newEdge(node6, node7, false);
Edge edge71=graphModel.factory().newEdge(node7, node1, false);
undirectedGraph.addEdge(edge12);
undirectedGraph.addEdge(edge23);
undirectedGraph.addEdge(edge31);
undirectedGraph.addEdge(edge14);
undirectedGraph.addEdge(edge45);
undirectedGraph.addEdge(edge51);