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) 2003-2007 |
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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 | \page maps2 Maps II. |
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21 | |
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22 | Here we discuss some advanced map techniques. Like writing your own maps or how to |
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23 | extend/modify a maps functionality with adaptors. |
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24 | |
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25 | \section custom_maps Writing Custom ReadMap |
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26 | \subsection custom_read_maps Readable Maps |
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27 | |
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28 | Readable maps are very frequently used as the input of an |
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29 | algorithm. For this purpose the most straightforward way is the use of the |
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30 | default maps provided by LEMON's graph structures. |
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31 | Very often however, it is more |
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32 | convenient and/or more efficient to write your own readable map. |
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33 | |
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34 | You can find some examples below. In these examples \c Graph is the |
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35 | type of the particular graph structure you use. |
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36 | |
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37 | |
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38 | This simple map assigns \f$\pi\f$ to each edge. |
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39 | |
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40 | \code |
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41 | struct MyMap |
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42 | { |
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43 | typedef double Value; |
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44 | typedef Graph::Edge Key; |
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45 | double operator[](const Key &e) const { return M_PI;} |
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46 | }; |
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47 | \endcode |
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48 | |
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49 | An alternative way to define maps is to use MapBase |
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50 | |
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51 | \code |
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52 | struct MyMap : public MapBase<Graph::Edge,double> |
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53 | { |
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54 | Value operator[](const Key& e) const { return M_PI;} |
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55 | }; |
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56 | \endcode |
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57 | |
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58 | Here is a bit more complex example. |
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59 | It provides a length function obtained |
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60 | from a base length function shifted by a potential difference. |
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61 | |
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62 | \code |
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63 | class ReducedLengthMap : public MapBase<Graph::Edge,double> |
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64 | { |
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65 | const Graph &g; |
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66 | const Graph::EdgeMap<double> &orig_len; |
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67 | const Graph::NodeMap<double> &pot; |
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68 | |
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69 | public: |
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70 | Value operator[](Key e) const { |
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71 | return orig_len[e]-(pot[g.target(e)]-pot[g.source(e)]); |
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72 | } |
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73 | |
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74 | ReducedLengthMap(const Graph &_g, |
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75 | const Graph::EdgeMap &_o, |
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76 | const Graph::NodeMap &_p) |
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77 | : g(_g), orig_len(_o), pot(_p) {}; |
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78 | }; |
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79 | \endcode |
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80 | |
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81 | Then, you can call e.g. Dijkstra algoritm on this map like this: |
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82 | \code |
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83 | ... |
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84 | ReducedLengthMap rm(g,len,pot); |
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85 | Dijkstra<Graph,ReducedLengthMap> dij(g,rm); |
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86 | dij.run(s); |
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87 | ... |
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88 | \endcode |
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89 | |
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90 | */ |
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