1 | /* -*- mode: C++; indent-tabs-mode: nil; -*- |
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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) 2003-2010 |
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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 | namespace lemon { |
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20 | /** |
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21 | [PAGE]sec_graph_structures[PAGE] Graph Structures |
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22 | |
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23 | The implementation of combinatorial algorithms heavily relies on |
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24 | efficient graph structures. Diverse applications require the |
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25 | usage of different physical graph storages. |
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26 | Until now, we used two general graph structures, \ref ListDigraph |
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27 | and \ref ListGraph. Apart from these types, LEMON also provides several |
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28 | other classes for handling directed and undirected graphs to meet the |
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29 | diverging requirements of the possible users. In order to save on running |
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30 | time or on memory usage, some structures may fail to support some graph |
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31 | features like node or arc/edge deletion. |
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32 | You are free to use the graph structure that fit your requirements the best, |
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33 | since most graph algorithms and auxiliary data structures can be used |
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34 | with any of them. |
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35 | |
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36 | |
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37 | [SEC]sec_graph_concepts[SEC] Graph Concepts |
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38 | |
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39 | In LEMON, there are various graph types, which are rather different, but |
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40 | they all conform to the corresponding \ref graph_concepts "graph concept", |
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41 | which defines the common part of the graph interfaces. |
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42 | The \ref concepts::Digraph "Digraph concept" describes the common interface |
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43 | of directed graphs (without any sensible implementation), while |
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44 | the \ref concepts::Graph "Graph concept" describes the undirected graphs. |
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45 | A generic graph algorithm should only exploit the features of the |
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46 | corresponding graph concept so that it could be applied to any graph |
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47 | structure. (Such an algorithm should compile with the |
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48 | \ref concepts::Digraph "Digraph" or \ref concepts::Graph "Graph" type, |
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49 | but it will not run properly, of course.) |
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50 | |
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51 | The graph %concepts define the member classes for the iterators and maps |
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52 | along with some useful basic functions for obtaining the identifiers of |
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53 | the items, the end nodes of the arcs (or edges) and their iterators, |
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54 | etc. |
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55 | An actual graph implementation may have various additional functionalities |
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56 | according to its purpose. |
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57 | |
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58 | Another advantage of this design is that you can write your own graph classes, |
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59 | if you would like to. |
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60 | As long as they provide the interface defined in one of the graph concepts, |
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61 | all the LEMON algorithms and classes will work with them properly. |
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62 | |
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63 | |
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64 | [SEC]sec_digraph_types[SEC] Directed Graph Structures |
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65 | |
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66 | The already used \ref ListDigraph class is the most versatile directed |
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67 | graph structure. As its name suggests, it is based on linked lists, |
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68 | therefore iterating through its nodes and arcs is fast and it is quite |
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69 | flexible. Apart from the general digraph functionalities, it |
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70 | provides operations for adding and removing nodes and arcs, changing |
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71 | the source or target node of an arc, and contracting and splitting nodes |
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72 | or arcs. |
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73 | |
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74 | \ref SmartDigraph is another general digraph implementation, which is |
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75 | significantly more efficient (both in terms of space and time), but it |
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76 | provides less functionality. For example, nodes and arcs cannot be |
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77 | removed from it. |
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78 | |
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79 | The \ref StaticDigraph structure is even more optimized for efficiency, |
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80 | but it is completely static. It requires less space in memory and |
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81 | provides faster item iteration than \ref ListDigraph and \ref |
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82 | SmartDigraph, especially using \ref concepts::Digraph::OutArcIt |
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83 | "OutArcIt" iterators, since its arcs are stored in an appropriate order. |
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84 | However, it only provides \ref StaticDigraph::build() "build()" and |
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85 | \ref \ref StaticDigraph::clear() "clear()" functions and does not |
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86 | support any other modification of the digraph. |
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87 | |
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88 | \ref FullDigraph is an efficient implementation of a directed full graph. |
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89 | This structure is also completely static, so you can neither add nor delete |
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90 | arcs or nodes, moreover, the class needs constant space in memory. |
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91 | |
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92 | |
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93 | [SEC]sec_graph_types[SEC] Undirected Graph Structures |
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94 | |
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95 | The general undirected graph classes, \ref ListGraph and \ref SmartGraph |
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96 | have similar implementations as their directed variants. |
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97 | Therefore, \ref SmartDigraph is more efficient, but \ref ListGraph provides |
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98 | more functionality. |
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99 | |
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100 | In addition to these general structures, LEMON also provides special purpose |
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101 | undirected graph types for handling \ref FullGraph "full graphs", |
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102 | \ref GridGraph "grid graphs" and \ref HypercubeGraph "hypercube graphs". |
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103 | They all static structures, i.e. they do not allow distinct item additions |
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104 | or deletions, the graph has to be built at once. |
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105 | |
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106 | [TRAILER] |
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107 | */ |
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108 | } |
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