/**
   * Check if the graph is chordal.
   *
   * @return true if the graph is chordal, false otherwise.
   */
  public boolean isChordal() {
    if (chordalGraph == null) {
      computeMinimalTriangulation();
    }

    return (chordalGraph.edgeSet().size() == graph.edgeSet().size());
  }
  /**
   * Create a copy of a graph for internal use.
   *
   * @param graph the graph to copy.
   * @return A copy of the graph projected to a SimpleGraph.
   */
  private static <V, E> UndirectedGraph<V, E> copyAsSimpleGraph(UndirectedGraph<V, E> graph) {
    UndirectedGraph<V, E> copy = new SimpleGraph<>(graph.getEdgeFactory());

    if (graph instanceof SimpleGraph) {
      Graphs.addGraph(copy, graph);
    } else {
      // project graph to SimpleGraph
      Graphs.addAllVertices(copy, graph.vertexSet());
      for (E e : graph.edgeSet()) {
        V v1 = graph.getEdgeSource(e);
        V v2 = graph.getEdgeTarget(e);
        if ((v1 != v2) && !copy.containsEdge(e)) {
          copy.addEdge(v1, v2);
        }
      }
    }
    return copy;
  }