[28] | 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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[32] | 5 | * Copyright (C) 2003-2010 |
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[28] | 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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[46] | 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] | 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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[32] | 41 | which defines the common part of the graph interfaces. |
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[28] | 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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[38] | 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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[28] | 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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[32] | 54 | etc. |
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[28] | 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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[38] | 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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[28] | 63 | |
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[46] | 64 | [SEC]sec_digraph_types[SEC] Directed Graph Structures |
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[28] | 65 | |
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| 66 | The already used \ref ListDigraph class is the most versatile directed |
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[38] | 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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[28] | 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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[32] | 77 | removed from it. |
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[28] | 78 | |
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[38] | 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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[50] | 84 | However, you can neither add nor delete arcs or nodes, the graph |
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| 85 | has to be built at once and other modifications are not supported. |
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[38] | 86 | |
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[28] | 87 | \ref FullDigraph is an efficient implementation of a directed full graph. |
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[50] | 88 | This structure is also completely static and it needs constant space |
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| 89 | in memory. |
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[28] | 90 | |
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| 91 | |
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[46] | 92 | [SEC]sec_graph_types[SEC] Undirected Graph Structures |
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[28] | 93 | |
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[46] | 94 | The general undirected graph classes, \ref ListGraph and \ref SmartGraph |
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| 95 | have similar implementations as their directed variants. |
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[50] | 96 | Therefore, \ref SmartGraph is more efficient, but \ref ListGraph provides |
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[46] | 97 | more functionality. |
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| 98 | In addition to these general structures, LEMON also provides special purpose |
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| 99 | undirected graph types for handling \ref FullGraph "full graphs", |
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| 100 | \ref GridGraph "grid graphs" and \ref HypercubeGraph "hypercube graphs". |
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[28] | 101 | |
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| 102 | [TRAILER] |
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| 103 | */ |
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| 104 | } |
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