1 | /* -*- C++ -*- |
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2 | * |
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3 | * This file is a part of LEMON, a generic C++ optimization library |
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4 | * |
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5 | * Copyright (C) 2003-2008 |
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6 | * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport |
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7 | * (Egervary Research Group on Combinatorial Optimization, EGRES). |
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8 | * |
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9 | * Permission to use, modify and distribute this software is granted |
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10 | * provided that this copyright notice appears in all copies. For |
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11 | * precise terms see the accompanying LICENSE file. |
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12 | * |
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13 | * This software is provided "AS IS" with no warranty of any kind, |
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14 | * express or implied, and with no claim as to its suitability for any |
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15 | * purpose. |
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16 | * |
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17 | */ |
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18 | |
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19 | /** |
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20 | @defgroup graph_adaptors Adaptor Classes for Graphs |
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21 | @ingroup graphs |
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22 | \brief This group contains several adaptor classes for graphs |
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23 | |
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24 | The main parts of LEMON are the different graph structures, |
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25 | generic graph algorithms, graph concepts which couple these, and |
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26 | graph adaptors. While the previous notions are more or less clear, the |
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27 | latter one needs further explanation. |
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28 | Graph adaptors are graph classes which serve for considering graph |
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29 | structures in different ways. |
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30 | |
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31 | A short example makes this much |
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32 | clearer. |
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33 | Suppose that we have an instance \c g of a directed graph |
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34 | type say ListGraph and an algorithm |
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35 | \code template<typename Graph> int algorithm(const Graph&); \endcode |
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36 | is needed to run on the reversed oriented graph. |
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37 | It may be expensive (in time or in memory usage) to copy |
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38 | \c g with the reversed orientation. |
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39 | In this case, an adaptor class is used, which |
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40 | (according to LEMON graph concepts) works as a graph. |
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41 | The adaptor uses |
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42 | the original graph structure and graph operations when methods of the |
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43 | reversed oriented graph are called. |
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44 | This means that the adaptor have minor memory usage, |
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45 | and do not perform sophisticated algorithmic actions. |
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46 | The purpose of it is to give a tool for the cases when |
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47 | a graph have to be used in a specific alteration. |
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48 | If this alteration is obtained by a usual construction |
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49 | like filtering the edge-set or considering a new orientation, then |
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50 | an adaptor is worthwhile to use. |
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51 | To come back to the reversed oriented graph, in this situation |
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52 | \code template<typename Graph> class RevGraphAdaptor; \endcode |
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53 | template class can be used. |
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54 | The code looks as follows |
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55 | \code |
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56 | ListGraph g; |
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57 | RevGraphAdaptor<ListGraph> rga(g); |
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58 | int result=algorithm(rga); |
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59 | \endcode |
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60 | After running the algorithm, the original graph \c g |
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61 | is untouched. |
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62 | This techniques gives rise to an elegant code, and |
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63 | based on stable graph adaptors, complex algorithms can be |
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64 | implemented easily. |
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65 | |
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66 | In flow, circulation and bipartite matching problems, the residual |
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67 | graph is of particular importance. Combining an adaptor implementing |
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68 | this, shortest path algorithms and minimum mean cycle algorithms, |
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69 | a range of weighted and cardinality optimization algorithms can be |
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70 | obtained. |
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71 | For other examples, |
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72 | the interested user is referred to the detailed documentation of |
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73 | particular adaptors. |
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74 | |
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75 | The behavior of graph adaptors can be very different. Some of them keep |
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76 | capabilities of the original graph while in other cases this would be |
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77 | meaningless. This means that the concepts that they are models of depend |
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78 | on the graph adaptor, and the wrapped graph(s). |
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79 | If an edge of \c rga is deleted, this is carried out by |
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80 | deleting the corresponding edge of \c g, thus the adaptor modifies the |
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81 | original graph. |
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82 | But for a residual |
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83 | graph, this operation has no sense. |
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84 | Let us stand one more example here to simplify your work. |
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85 | RevGraphAdaptor has constructor |
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86 | \code |
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87 | RevGraphAdaptor(Graph& _g); |
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88 | \endcode |
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89 | This means that in a situation, |
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90 | when a <tt> const ListGraph& </tt> reference to a graph is given, |
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91 | then it have to be instantiated with <tt>Graph=const ListGraph</tt>. |
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92 | \code |
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93 | int algorithm1(const ListGraph& g) { |
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94 | RevGraphAdaptor<const ListGraph> rga(g); |
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95 | return algorithm2(rga); |
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96 | } |
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97 | \endcode |
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98 | */ |
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