private SimpleGraph<DefaultVertex, DefaultEdge<DefaultVertex>> constructLineGraph() {
SimpleGraph<DefaultVertex, DefaultEdge<DefaultVertex>> lg =
new SimpleGraph<DefaultVertex, DefaultEdge<DefaultVertex>>(graph.getEdgeFactory());
HashMap<DefaultVertex, DefaultEdge<DefaultVertex>> map =
new HashMap<DefaultVertex, DefaultEdge<DefaultVertex>>();
for (DefaultEdge<DefaultVertex> e : graph.edgeSet()) {
DefaultVertex v = getMidPoint(e.getSource(), e.getTarget());
lg.addVertex(v);
map.put(v, e);
}
for (DefaultVertex v1 : lg.vertexSet()) {
for (DefaultVertex v2 : lg.vertexSet()) {
if (v1 == v2 || lg.containsEdge(v1, v2)) continue;
DefaultEdge<DefaultVertex> e1 = map.get(v1);
DefaultEdge<DefaultVertex> e2 = map.get(v2);
if (Neighbors.isIncidentEdge(graph, e1, e2)) lg.addEdge(v1, v2);
}
}
return lg;
}