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kpeter (Peter Kovacs)
kpeter@inf.elte.hu
Faster computation of the dual solution in CostScaling (#417)
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1 file changed with 54 insertions and 26 deletions:
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Show white space 6 line context
... ...
@@ -239,3 +239,2 @@
239 239

	
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    typedef StaticVectorMap<StaticDigraph::Node, LargeCost> LargeCostNodeMap;
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    typedef StaticVectorMap<StaticDigraph::Arc, LargeCost> LargeCostArcMap;
... ...
@@ -290,10 +289,2 @@
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    // Data for a StaticDigraph structure
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    typedef std::pair<int, int> IntPair;
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    StaticDigraph _sgr;
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    std::vector<IntPair> _arc_vec;
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    std::vector<LargeCost> _cost_vec;
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    LargeCostArcMap _cost_map;
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    LargeCostNodeMap _pi_map;
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  public:
... ...
@@ -344,3 +335,2 @@
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      _graph(graph), _node_id(graph), _arc_idf(graph), _arc_idb(graph),
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      _cost_map(_cost_vec), _pi_map(_pi),
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      INF(std::numeric_limits<Value>::has_infinity ?
... ...
@@ -621,5 +611,2 @@
621 611

	
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      _arc_vec.reserve(_res_arc_num);
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      _cost_vec.reserve(_res_arc_num);
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      // Copy the graph
... ...
@@ -925,18 +912,59 @@
925 912

	
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      // Compute node potentials for the original costs
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      _arc_vec.clear();
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      _cost_vec.clear();
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      for (int j = 0; j != _res_arc_num; ++j) {
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        if (_res_cap[j] > 0) {
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          _arc_vec.push_back(IntPair(_source[j], _target[j]));
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          _cost_vec.push_back(_scost[j]);
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      // Compute node potentials (dual solution)
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      for (int i = 0; i != _res_node_num; ++i) {
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        _pi[i] = static_cast<Cost>(_pi[i] / (_res_node_num * _alpha));
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      }
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      bool optimal = true;
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      for (int i = 0; optimal && i != _res_node_num; ++i) {
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        LargeCost pi_i = _pi[i];
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        int last_out = _first_out[i+1];
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        for (int j = _first_out[i]; j != last_out; ++j) {
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          if (_res_cap[j] > 0 && _scost[j] + pi_i - _pi[_target[j]] < 0) {
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            optimal = false;
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            break;
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          }
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        }
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      }
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      _sgr.build(_res_node_num, _arc_vec.begin(), _arc_vec.end());
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      typename BellmanFord<StaticDigraph, LargeCostArcMap>
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        ::template SetDistMap<LargeCostNodeMap>::Create bf(_sgr, _cost_map);
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      bf.distMap(_pi_map);
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      bf.init(0);
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      bf.start();
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      if (!optimal) {
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        // Compute node potentials for the original costs with BellmanFord
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        // (if it is necessary)
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        typedef std::pair<int, int> IntPair;
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        StaticDigraph sgr;
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        std::vector<IntPair> arc_vec;
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        std::vector<LargeCost> cost_vec;
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        LargeCostArcMap cost_map(cost_vec);
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        arc_vec.clear();
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        cost_vec.clear();
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        for (int j = 0; j != _res_arc_num; ++j) {
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          if (_res_cap[j] > 0) {
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            int u = _source[j], v = _target[j];
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            arc_vec.push_back(IntPair(u, v));
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            cost_vec.push_back(_scost[j] + _pi[u] - _pi[v]);
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          }
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        }
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        sgr.build(_res_node_num, arc_vec.begin(), arc_vec.end());
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        typename BellmanFord<StaticDigraph, LargeCostArcMap>::Create
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          bf(sgr, cost_map);
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        bf.init(0);
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        bf.start();
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        for (int i = 0; i != _res_node_num; ++i) {
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          _pi[i] += bf.dist(sgr.node(i));
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        }
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      }
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      // Shift potentials to meet the requirements of the GEQ type
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      // optimality conditions
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      LargeCost max_pot = _pi[_root];
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      for (int i = 0; i != _res_node_num; ++i) {
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        if (_pi[i] > max_pot) max_pot = _pi[i];
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      }
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      if (max_pot != 0) {
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        for (int i = 0; i != _res_node_num; ++i) {
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          _pi[i] -= max_pot;
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        }
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      }
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