1 | // -*- c++ -*- |
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2 | #include <iostream> |
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3 | #include <fstream> |
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4 | |
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5 | #include <lemon/smart_graph.h> |
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6 | #include <lemon/list_graph.h> |
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7 | #include <lemon/dimacs.h> |
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8 | #include <lemon/time_measure.h> |
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9 | #include <lp_solver_base.h> |
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10 | |
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11 | using std::cout; |
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12 | using std::endl; |
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13 | using namespace lemon; |
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14 | |
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15 | template<typename Edge, typename EdgeIndexMap> |
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16 | class PrimalMap { |
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17 | protected: |
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18 | LPGLPK* lp; |
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19 | EdgeIndexMap* edge_index_map; |
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20 | public: |
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21 | PrimalMap(LPGLPK& _lp, EdgeIndexMap& _edge_index_map) : |
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22 | lp(&_lp), edge_index_map(&_edge_index_map) { } |
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23 | double operator[](Edge e) const { |
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24 | return lp->getPrimal((*edge_index_map)[e]); |
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25 | } |
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26 | }; |
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27 | |
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28 | // Use a DIMACS max flow file as stdin. |
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29 | // max_flow_expresion < dimacs_max_flow_file |
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30 | |
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31 | int main(int, char **) { |
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32 | |
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33 | typedef ListGraph Graph; |
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34 | typedef Graph::Node Node; |
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35 | typedef Graph::Edge Edge; |
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36 | typedef Graph::EdgeIt EdgeIt; |
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37 | |
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38 | Graph g; |
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39 | |
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40 | Node s, t; |
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41 | Graph::EdgeMap<int> cap(g); |
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42 | readDimacs(std::cin, g, cap, s, t); |
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43 | Timer ts; |
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44 | |
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45 | typedef LPGLPK LPSolver; |
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46 | LPSolver lp; |
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47 | lp.setMaximize(); |
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48 | typedef LPSolver::ColIt ColIt; |
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49 | typedef LPSolver::RowIt RowIt; |
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50 | typedef Graph::EdgeMap<ColIt> EdgeIndexMap; |
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51 | EdgeIndexMap edge_index_map(g); |
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52 | PrimalMap<Edge, EdgeIndexMap> flow(lp, edge_index_map); |
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53 | |
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54 | // nonnegativity of flow and capacity function |
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55 | for (Graph::EdgeIt e(g); e!=INVALID; ++e) { |
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56 | ColIt col_it=lp.addCol(); |
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57 | edge_index_map.set(e, col_it); |
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58 | // interesting property in GLPK: |
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59 | // if you change the order of the following two lines, the |
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60 | // two runs of GLPK are extremely different |
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61 | lp.setColLowerBound(col_it, 0); |
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62 | lp.setColUpperBound(col_it, cap[e]); |
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63 | } |
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64 | |
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65 | for (Graph::NodeIt n(g); n!=INVALID; ++n) { |
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66 | LPSolver::Expression expr; |
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67 | for (Graph::OutEdgeIt e(g, n); e!=INVALID; ++e) |
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68 | expr+=edge_index_map[e]; |
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69 | for (Graph::InEdgeIt e(g, n); e!=INVALID; ++e) |
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70 | expr-=edge_index_map[e]; |
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71 | // cost function |
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72 | if (n==s) { |
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73 | lp.setObjCoeffs(expr); |
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74 | } |
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75 | // flow conservation constraints |
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76 | if ((n!=s) && (n!=t)) { |
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77 | RowIt row_it=lp.addRow(); |
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78 | lp.setRowCoeffs(row_it, expr); |
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79 | lp.setRowLowerBound(row_it, 0.0); |
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80 | lp.setRowUpperBound(row_it, 0.0); |
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81 | } |
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82 | } |
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83 | lp.solveSimplex(); |
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84 | cout << "elapsed time: " << ts << endl; |
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85 | } |
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