73 lines
3.0 KiB
C++
73 lines
3.0 KiB
C++
#include <minizinc/algorithms/min_cut.h>
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#include <minizinc/config.hh>
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#include <stdexcept>
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#ifdef COMPILE_BOOST_MINCUT
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#include <boost/graph/adjacency_list.hpp>
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#include <boost/graph/graph_traits.hpp>
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#include <boost/graph/one_bit_color_map.hpp>
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#include <boost/graph/stoer_wagner_min_cut.hpp>
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#include <boost/property_map/property_map.hpp>
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#include <boost/typeof/typeof.hpp>
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#endif
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void Algorithms::MinCut::solve() {
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#ifndef COMPILE_BOOST_MINCUT
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throw std::runtime_error(
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"MIP/circuit: Subtour Elimination Constraints: MinCut::solve not compiled. "
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"Compile with COMPILE_BOOST_MINCUT (needs boost), or use -D nSECcuts=0 for flattening.");
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#else
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typedef std::pair<unsigned long, unsigned long> edge_t;
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// A graphic of the min-cut is available at
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// <http://www.boost.org/doc/libs/release/libs/graph/doc/stoer_wagner_imgs/stoer_wagner.cpp.gif>
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using namespace std;
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typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, boost::no_property,
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boost::property<boost::edge_weight_t, double> >
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undirected_graph;
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typedef boost::property_map<undirected_graph, boost::edge_weight_t>::type weight_map_type;
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typedef boost::property_traits<weight_map_type>::value_type weight_type;
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// define the 16 edges of the graph. {3, 4} means an undirected edge between vertices 3 and 4.
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// edge_t edges[] = {{3, 4}, {3, 6}, {3, 5}, {0, 4}, {0, 1}, {0, 6}, {0, 7},
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// {0, 5}, {0, 2}, {4, 1}, {1, 6}, {1, 5}, {6, 7}, {7, 5}, {5, 2}, {3, 4}};
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std::vector<edge_t> edges_array; // = edges;
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// std::vector< weight_type > ws_array;
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edges_array.reserve(edges.size());
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for (const auto& edg : edges)
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edges_array.push_back(std::pair<unsigned long, unsigned long>(edg.first, edg.second));
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// for each of the 16 edges, define the associated edge weight. ws[i] is the weight for the edge
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// that is described by edges[i].
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// weight_type ws[] =
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// {0.2, 3.1, 1.3, 3.7, 1.5, 2.6, 6.44, 1.26, 8.77, 1.29, 1.95, 80.74, 2.23, 1.94, 1.23, 4.957};
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// construct the graph object. 8 is the number of vertices, which are numbered from 0
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// through 7, and 16 is the number of edges.
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undirected_graph g(edges_array.data(), edges_array.data() + edges_array.size(), weights.data(),
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nNodes, edges_array.size());
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// define a property map, `parities`, that will store a boolean value for each vertex.
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// Vertices that have the same parity after `stoer_wagner_min_cut` runs are on the same side of
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// the min-cut.
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BOOST_AUTO(parities00,
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boost::make_one_bit_color_map(num_vertices(g), get(boost::vertex_index, g)));
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// run the Stoer-Wagner algorithm to obtain the min-cut weight. `parities` is also filled in.
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wMinCut =
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boost::stoer_wagner_min_cut(g, get(boost::edge_weight, g), boost::parity_map(parities00));
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assert(nNodes == num_vertices(g));
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// parities = parities00;
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parities.clear();
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parities.reserve(nNodes);
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for (size_t i = 0; i < num_vertices(g); ++i) {
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parities.push_back(get(parities00, i));
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}
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#endif
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}
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