LongPrimitiveIterator items1 = dataModel.getItemIDs();
    LongPrimitiveIterator items2 = dataModel.getItemIDs();
    while(items1.hasNext()){
      Long i1 = items1.next();
      while(items2.hasNext()){
        Long i2 = items2.next();
        double res = itemSimilarity.itemSimilarity(i1, i2);
        System.out.println("["+i1+"]["+i2+"] "+res );
      }
    }