1 | /** |
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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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4 | @ingroup graphs |
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5 | |
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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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8 | graph adaptors. While the previous notions are more or less clear, the |
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9 | latter one needs further explanation. |
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10 | Graph adaptors are graph classes which serve for considering graph |
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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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14 | clearer. |
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15 | Suppose that we have an instance \c g of a directed graph |
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16 | type say ListGraph and an algorithm |
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17 | \code template<typename Graph> int algorithm(const Graph&); \endcode |
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18 | is needed to run on the reversed oriented graph. |
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19 | It may be expensive (in time or in memory usage) to copy |
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20 | \c g with the reversed orientation. |
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21 | In this case, an adaptor class is used, which |
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22 | (according to LEMON graph concepts) works as a graph. |
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23 | The adaptor 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 adaptor 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 | an adaptor 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 RevGraphAdaptor; \endcode |
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35 | template class can be used. |
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36 | The code looks as follows |
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37 | \code |
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38 | ListGraph g; |
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39 | RevGraphAdaptor<ListGraph> rgw(g); |
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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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43 | is untouched. |
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44 | This techniques gives rise to an elegant code, and |
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45 | based on stable graph adaptors, complex algorithms can be |
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46 | implemented easily. |
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47 | |
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48 | In flow, circulation and bipartite matching problems, the residual |
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49 | graph is of particular importance. Combining an adaptor implementing |
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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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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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55 | particular adaptors. |
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56 | |
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57 | The behavior of graph adaptors can be very different. Some of them keep |
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58 | capabilities of the original graph while in other cases this would be |
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59 | meaningless. This means that the concepts that they are models of depend |
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60 | on the graph adaptor, and the wrapped graph(s). |
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61 | If an edge of \c rgw is deleted, this is carried out by |
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62 | deleting the corresponding edge of \c g, thus the adaptor modifies the |
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63 | original graph. |
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64 | But for a residual |
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65 | graph, this operation has no sense. |
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66 | Let us stand one more example here to simplify your work. |
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67 | RevGraphAdaptor has constructor |
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68 | \code |
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69 | RevGraphAdaptor(Graph& _g); |
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70 | \endcode |
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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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76 | RevGraphAdaptor<const ListGraph> rgw(g); |
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77 | return algorithm2(rgw); |
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78 | } |
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79 | \endcode |
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80 | */ |
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