Example #1
0
 /**
  * This returns an enumeration of all Darts in Graph G in a canonical order starting with
  * firstDart. The order is canonical in the sense that it only depends on the oriented isomorphism
  * class of G (and firstDart). That is, if there is an oriented iso G <-> G' sending firstDart <->
  * firstDart', then that bijection will send getDarts <-> getDarts'.
  *
  * <p>This enumeration is useful in finding explicit bijections of isomorphic graphs.
  */
 public static Dart[] getDarts(Dart firstDart, Graph G) {
   /**
    * Description of algorithm: Return all the couples around V0=firstDart.V, then all couples
    * around V1, .... The order for couples around firstDart.V is counterclockwise starting with
    * firstDart.F. clockwise around V1,... So we need to order the vertices V0,V1,... and pick the
    * first face to use at each vertex and the rest is determined. Order on V0,... = first
    * encountered. Order on faces at vertex = first encountered.
    */
   distinctFIFO vQueue = new distinctFIFO();
   util.ConditionGetter fQueue = new util.ConditionGetter();
   fQueue.add(firstDart.getF());
   vQueue.put(firstDart.getV());
   Collection coups = new ArrayList();
   int coupsIndex = 0;
   Vertex V;
   while ((V = (Vertex) vQueue.remove()) != null) {
     Face F = (Face) fQueue.get(new incidence(V));
     for (int i = 0; i < V.size(); i++) {
       Face Fx = V.next(F, i);
       coups.add(new Dart(V, Fx));
       vQueue.put(Fx.next(V, 1));
       fQueue.add(Fx);
     }
   }
   return (Dart[]) coups.toArray(new Dart[coups.size()]);
 }
Example #2
0
 public void testDart() {
   String S = Formatter.testString; // see formatterString.gif
   Graph G = Graph.getInstance(new Formatter(S));
   Vertex V = null;
   int coupleCount = 0;
   for (Enumeration E = G.vertexEnumeration(); E.hasMoreElements(); /*--*/ ) {
     Vertex W = (Vertex) E.nextElement();
     coupleCount += W.size();
     if (W.size() == 3) V = W;
   }
   jassert(V.size() == 3);
   Face F = V.getAny();
   while (F.size() != 5) F = V.next(F, 1);
   jassert(F.size() == 5);
   Dart C = new Dart(V, F);
   Dart[] list = Dart.getDarts(C, G);
   // compute the expected number of return values;
   jassert(list.length == coupleCount);
   jassert(list[0].getV() == C.getV());
   jassert(list[0].getF() == C.getF());
   // check integrity of each couple.
   for (int i = 0; i < list.length; i++) {
     V = list[i].getV();
     F = list[i].getF();
     jassert(V.next(F, 0) == F);
     jassert(F.next(V, 0) == V);
   }
   // check that all couples are distinct.
   Hashtable table = new Hashtable(); // { V-> set of F }
   for (Enumeration E = G.vertexEnumeration(); E.hasMoreElements(); /*--*/ ) {
     V = (Vertex) E.nextElement();
     table.put(V, new HashSet());
   }
   for (int i = 0; i < list.length; i++) {
     V = list[i].getV();
     F = list[i].getF();
     HashSet H = (HashSet) table.get(V);
     jassert(!H.contains(F));
     H.add(F);
   }
 }