1 /** |
|
2 @defgroup gwrappers Wrapper Classes for Graphs |
|
3 \brief This group contains several wrapper classes for graphs |
|
4 @ingroup graphs |
|
5 |
|
6 The main parts of LEMON are the different graph structures, |
|
7 generic graph algorithms, graph concepts which couple these, and |
|
8 graph wrappers. While the previous notions are more or less clear, the |
|
9 latter one needs further explanation. |
|
10 Graph wrappers are graph classes which serve for considering graph |
|
11 structures in different ways. |
|
12 |
|
13 A short example makes this much |
|
14 clearer. |
|
15 Suppose that we have an instance \c g of a directed graph |
|
16 type say ListGraph and an algorithm |
|
17 \code template<typename Graph> int algorithm(const Graph&); \endcode |
|
18 is needed to run on the reversed oriented graph. |
|
19 It may be expensive (in time or in memory usage) to copy |
|
20 \c g with the reversed orientation. |
|
21 In this case, a wrapper class is used, which |
|
22 (according to LEMON graph concepts) works as a graph. |
|
23 The wrapper uses |
|
24 the original graph structure and graph operations when methods of the |
|
25 reversed oriented graph are called. |
|
26 This means that the wrapper have minor memory usage, |
|
27 and do not perform sophisticated algorithmic actions. |
|
28 The purpose of it is to give a tool for the cases when |
|
29 a graph have to be used in a specific alteration. |
|
30 If this alteration is obtained by a usual construction |
|
31 like filtering the edge-set or considering a new orientation, then |
|
32 a wrapper is worthwhile to use. |
|
33 To come back to the reversed oriented graph, in this situation |
|
34 \code template<typename Graph> class RevGraphWrapper; \endcode |
|
35 template class can be used. |
|
36 The code looks as follows |
|
37 \code |
|
38 ListGraph g; |
|
39 RevGraphWrapper<ListGraph> rgw(g); |
|
40 int result=algorithm(rgw); |
|
41 \endcode |
|
42 After running the algorithm, the original graph \c g |
|
43 is untouched. |
|
44 This techniques gives rise to an elegant code, and |
|
45 based on stable graph wrappers, complex algorithms can be |
|
46 implemented easily. |
|
47 |
|
48 In flow, circulation and bipartite matching problems, the residual |
|
49 graph is of particular importance. Combining a wrapper implementing |
|
50 this, shortest path algorithms and minimum mean cycle algorithms, |
|
51 a range of weighted and cardinality optimization algorithms can be |
|
52 obtained. |
|
53 For other examples, |
|
54 the interested user is referred to the detailed documentation of |
|
55 particular wrappers. |
|
56 |
|
57 The behavior of graph wrappers can be very different. Some of them keep |
|
58 capabilities of the original graph while in other cases this would be |
|
59 meaningless. This means that the concepts that they are models of depend |
|
60 on the graph wrapper, and the wrapped graph(s). |
|
61 If an edge of \c rgw is deleted, this is carried out by |
|
62 deleting the corresponding edge of \c g, thus the wrapper modifies the |
|
63 original graph. |
|
64 But for a residual |
|
65 graph, this operation has no sense. |
|
66 Let us stand one more example here to simplify your work. |
|
67 RevGraphWrapper has constructor |
|
68 \code |
|
69 RevGraphWrapper(Graph& _g); |
|
70 \endcode |
|
71 This means that in a situation, |
|
72 when a <tt> const ListGraph& </tt> reference to a graph is given, |
|
73 then it have to be instantiated with <tt>Graph=const ListGraph</tt>. |
|
74 \code |
|
75 int algorithm1(const ListGraph& g) { |
|
76 RevGraphWrapper<const ListGraph> rgw(g); |
|
77 return algorithm2(rgw); |
|
78 } |
|
79 \endcode |
|
80 */ |
|