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