1 | /* -*- C++ -*- |
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2 | * demo/tight_edge_filter_map.h - Part of LEMON, a generic C++ optimization |
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3 | * library |
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4 | * |
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5 | * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport |
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6 | * (Egervary Research Group on Combinatorial Optimization, EGRES). |
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7 | * |
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8 | * Permission to use, modify and distribute this software is granted |
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9 | * provided that this copyright notice appears in all copies. For |
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10 | * precise terms see the accompanying LICENSE file. |
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11 | * |
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12 | * This software is provided "AS IS" with no warranty of any kind, |
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13 | * express or implied, and with no claim as to its suitability for any |
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14 | * purpose. |
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15 | * |
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16 | */ |
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17 | |
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18 | #ifndef LEMON_TIGHT_EDGE_FILTER_MAP_H |
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19 | #define LEMON_TIGHT_EDGE_FILTER_MAP_H |
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20 | |
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21 | #include <lemon/maps.h> |
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22 | |
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23 | // /// \file |
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24 | // /// \brief Maximum flow algorithms. |
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25 | // /// \ingroup galgs |
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26 | |
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27 | namespace lemon { |
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28 | |
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29 | /*! |
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30 | \brief A map for filtering the edge-set to those edges |
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31 | which are tight w.r.t. a node-potential and |
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32 | edge-distance. |
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33 | |
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34 | Let \f$G=(V,A)\f$ be a directed graph (graph for short) and |
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35 | let \f$\mathbb{F}\f$ be a number type. |
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36 | Given a distance function |
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37 | \f$d:E\to\mathbb{F}\f$, |
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38 | \f$\pi:V\to\mathbb{F}\f$ is said to be a potetial |
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39 | w.r.t. \f$d\f$ |
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40 | if and only if |
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41 | \f$\pi(v)\le d(uv)+\pi(u)\f$ holds for each edge \f$uv\in E\f$ |
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42 | (or the reverse inequality holds for each edge). |
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43 | An edge is said to be tight if this inequality holds with equality, |
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44 | and the map returns \c true exactly for those edges. |
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45 | To avoid rounding errors, it is recommended to use this class with exact |
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46 | number types, e.g. with \c int. |
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47 | */ |
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48 | template<typename Graph, |
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49 | typename NodePotentialMap, typename EdgeDistanceMap> |
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50 | class TightEdgeFilterMap : public MapBase<typename Graph::Edge, bool> { |
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51 | protected: |
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52 | const Graph* g; |
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53 | NodePotentialMap* node_potential; |
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54 | EdgeDistanceMap* edge_distance; |
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55 | public: |
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56 | TightEdgeFilterMap(Graph& _g, NodePotentialMap& _node_potential, |
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57 | EdgeDistanceMap& _edge_distance) : |
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58 | g(&_g), node_potential(&_node_potential), |
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59 | edge_distance(&_edge_distance) { } |
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60 | bool operator[](const typename Graph::Edge& e) const { |
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61 | return ((*node_potential)[g->target(e)] == |
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62 | (*edge_distance)[e]+(*node_potential)[g->source(e)]); |
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63 | } |
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64 | }; |
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65 | |
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66 | } //namespace lemon |
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67 | |
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68 | #endif //LEMON_TIGHT_EDGE_FILTER_MAP_H |
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