[1172] | 1 | /** |
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[1401] | 2 | @defgroup graph_adaptors Adaptor Classes for Graphs |
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| 3 | \brief This group contains several adaptor classes for graphs |
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[1172] | 4 | @ingroup graphs |
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[556] | 5 | |
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[1172] | 6 | The main parts of LEMON are the different graph structures, |
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| 7 | generic graph algorithms, graph concepts which couple these, and |
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[1401] | 8 | graph adaptors. While the previous notions are more or less clear, the |
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[1252] | 9 | latter one needs further explanation. |
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[1401] | 10 | Graph adaptors are graph classes which serve for considering graph |
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[1252] | 11 | structures in different ways. |
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| 12 | |
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| 13 | A short example makes this much |
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[1172] | 14 | clearer. |
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| 15 | Suppose that we have an instance \c g of a directed graph |
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[1252] | 16 | type say ListGraph and an algorithm |
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[1172] | 17 | \code template<typename Graph> int algorithm(const Graph&); \endcode |
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[1252] | 18 | is needed to run on the reversed oriented graph. |
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[1172] | 19 | It may be expensive (in time or in memory usage) to copy |
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[1252] | 20 | \c g with the reversed orientation. |
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[1401] | 21 | In this case, an adaptor class is used, which |
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[1252] | 22 | (according to LEMON graph concepts) works as a graph. |
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[1401] | 23 | The adaptor uses |
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[1252] | 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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[1401] | 26 | This means that the adaptor have minor memory usage, |
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[1252] | 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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[1401] | 32 | an adaptor is worthwhile to use. |
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[1252] | 33 | To come back to the reversed oriented graph, in this situation |
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[1401] | 34 | \code template<typename Graph> class RevGraphAdaptor; \endcode |
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[1252] | 35 | template class can be used. |
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| 36 | The code looks as follows |
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[1172] | 37 | \code |
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| 38 | ListGraph g; |
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[1401] | 39 | RevGraphAdaptor<ListGraph> rgw(g); |
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[1172] | 40 | int result=algorithm(rgw); |
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| 41 | \endcode |
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| 42 | After running the algorithm, the original graph \c g |
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[1252] | 43 | is untouched. |
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[1172] | 44 | This techniques gives rise to an elegant code, and |
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[1401] | 45 | based on stable graph adaptors, complex algorithms can be |
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[1172] | 46 | implemented easily. |
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[1252] | 47 | |
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[1172] | 48 | In flow, circulation and bipartite matching problems, the residual |
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[1401] | 49 | graph is of particular importance. Combining an adaptor implementing |
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[1172] | 50 | this, shortest path algorithms and minimum mean cycle algorithms, |
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| 51 | a range of weighted and cardinality optimization algorithms can be |
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[1252] | 52 | obtained. |
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| 53 | For other examples, |
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| 54 | the interested user is referred to the detailed documentation of |
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[1401] | 55 | particular adaptors. |
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[1252] | 56 | |
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[1401] | 57 | The behavior of graph adaptors can be very different. Some of them keep |
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[1172] | 58 | capabilities of the original graph while in other cases this would be |
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[1252] | 59 | meaningless. This means that the concepts that they are models of depend |
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[1401] | 60 | on the graph adaptor, and the wrapped graph(s). |
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[1172] | 61 | If an edge of \c rgw is deleted, this is carried out by |
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[1401] | 62 | deleting the corresponding edge of \c g, thus the adaptor modifies the |
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[1252] | 63 | original graph. |
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| 64 | But for a residual |
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[1172] | 65 | graph, this operation has no sense. |
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[1252] | 66 | Let us stand one more example here to simplify your work. |
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[1401] | 67 | RevGraphAdaptor has constructor |
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[1252] | 68 | \code |
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[1401] | 69 | RevGraphAdaptor(Graph& _g); |
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[1252] | 70 | \endcode |
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[1172] | 71 | This means that in a situation, |
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| 72 | when a <tt> const ListGraph& </tt> reference to a graph is given, |
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| 73 | then it have to be instantiated with <tt>Graph=const ListGraph</tt>. |
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| 74 | \code |
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| 75 | int algorithm1(const ListGraph& g) { |
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[1401] | 76 | RevGraphAdaptor<const ListGraph> rgw(g); |
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[1172] | 77 | return algorithm2(rgw); |
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| 78 | } |
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| 79 | \endcode |
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| 80 | */ |
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