LEMON/LEMON-main Changeset - r853:ec0b1b423b8b

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Changeset - r853:ec0b1b423b8b

« 852:30c77d

854:9a7e4e »

r853:ec0b1b423b8b

Fri, 16 Oct 2009 01:06:16

[Not Reviewed]

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kpeter (Peter Kovacs)
kpeter@inf.elte.hu

Rework and improve Suurballe (#323) - Improve the implementation: use a specific, faster variant of residual Dijkstra for the first search. - Some reorganizatiopn to make the code simpler. - Small doc improvements.

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1 file changed with 94 insertions and 58 deletions:

lemon/suurballe.h

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lemon/suurballe.h

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@@ -46,7 +46,7 @@
 		  /// Note that this problem is a special case of the \ref min_cost_flow
 		  /// "minimum cost flow problem". This implementation is actually an
 		  /// efficient specialized version of the \ref CapacityScaling
-		  /// "Successive Shortest Path" algorithm directly for this problem.
+		  /// "successive shortest path" algorithm directly for this problem.
 		  /// Therefore this class provides query functions for flow values and
 		  /// node potentials (the dual solution) just like the minimum cost flow
 		  /// algorithms.
@@ -57,7 +57,7 @@
 		  ///
 		  /// \warning Length values should be \e non-negative.
 		  ///
 		  /// \note For finding node-disjoint paths this algorithm can be used
+		  /// \note For finding \e node-disjoint paths, this algorithm can be used
 		  /// along with the \ref SplitNodes adaptor.
 		#ifdef DOXYGEN
 		  template <typename GR, typename LEN>
@@ -109,39 +109,36 @@
 		    private:
 		      // The digraph the algorithm runs on
 		      const Digraph &_graph;
 		      // The main maps
 		      const LengthMap &_length;
 		      const FlowMap &_flow;
 		      const LengthMap &_length;
 		      PotentialMap &_potential;
 		      // The distance map
 		      PotentialMap _dist;
 		      // The pred arc map
 		      PotentialMap &_pi;
 		      PredMap &_pred;
 		      // The processed (i.e. permanently labeled) nodes
 		      std::vector<Node> _proc_nodes;
 		      Node _s;
 		      Node _t;
 		      PotentialMap _dist;
 		      std::vector<Node> _proc_nodes;
 		    public:
 		      /// Constructor.
 		      ResidualDijkstra( const Digraph &graph,
 		                        const FlowMap &flow,
 		                        const LengthMap &length,
 		                        PotentialMap &potential,
 		                        PredMap &pred,
 		                        Node s, Node t ) :
 		        _graph(graph), _flow(flow), _length(length), _potential(potential),
-		        _dist(graph), _pred(pred), _s(s), _t(t) {}
+		      // Constructor
 		      ResidualDijkstra(Suurballe &srb) :
 		        _graph(srb._graph), _length(srb._length),
 		        _flow(*srb._flow), _pi(*srb._potential), _pred(srb._pred),
 		        _s(srb._s), _t(srb._t), _dist(_graph) {}
 		      /// \brief Run the algorithm. It returns \c true if a path is found
 		      /// from the source node to the target node.
-		      bool run() {
+		      // Run the algorithm and return true if a path is found
 		      // from the source node to the target node.
 		      bool run(int cnt) {
 		        return cnt == 0 ? startFirst() : start();
+		      }
 		    private:
 		      // Execute the algorithm for the first time (the flow and potential
 		      // functions have to be identically zero).
 		      bool startFirst() {
 		        HeapCrossRef heap_cross_ref(_graph, Heap::PRE_HEAP);
 		        Heap heap(heap_cross_ref);
 		        heap.push(_s, 0);
@@ -151,10 +148,55 @@
 		        // Process nodes
 		        while (!heap.empty() && heap.top() != _t) {
 		          Node u = heap.top(), v;
-		          Length d = heap.prio() + _potential[u], nd;
+		          Length d = heap.prio(), dn;
 		          _dist[u] = heap.prio();
 		          _proc_nodes.push_back(u);
 		          heap.pop();
 		          // Traverse outgoing arcs
 		          for (OutArcIt e(_graph, u); e != INVALID; ++e) {
 		            v = _graph.target(e);
 		            switch(heap.state(v)) {
 		              case Heap::PRE_HEAP:
 		                heap.push(v, d + _length[e]);
 		                _pred[v] = e;
 		                break;
 		              case Heap::IN_HEAP:
 		                dn = d + _length[e];
 		                if (dn < heap[v]) {
 		                  heap.decrease(v, dn);
 		                  _pred[v] = e;
+		                }
 		                break;
 		              case Heap::POST_HEAP:
 		                break;
+		            }
+		          }
+		        }
 		        if (heap.empty()) return false;
 		        // Update potentials of processed nodes
 		        Length t_dist = heap.prio();
 		        for (int i = 0; i < int(_proc_nodes.size()); ++i)
 		          _pi[_proc_nodes[i]] = _dist[_proc_nodes[i]] - t_dist;
 		        return true;
+		      }
 		      // Execute the algorithm.
 		      bool start() {
 		        HeapCrossRef heap_cross_ref(_graph, Heap::PRE_HEAP);
 		        Heap heap(heap_cross_ref);
 		        heap.push(_s, 0);
 		        _pred[_s] = INVALID;
 		        _proc_nodes.clear();
 		        // Process nodes
 		        while (!heap.empty() && heap.top() != _t) {
 		          Node u = heap.top(), v;
 		          Length d = heap.prio() + _pi[u], dn;
 		          _dist[u] = heap.prio();
 		          _proc_nodes.push_back(u);
 		          heap.pop();
 		          // Traverse outgoing arcs
 		          for (OutArcIt e(_graph, u); e != INVALID; ++e) {
@@ -162,13 +204,13 @@
 		              v = _graph.target(e);
 		              switch(heap.state(v)) {
 		              case Heap::PRE_HEAP:
-		                heap.push(v, d + _length[e] - _potential[v]);
+		                  heap.push(v, d + _length[e] - _pi[v]);
 		                _pred[v] = e;
 		                break;
 		              case Heap::IN_HEAP:
 		                nd = d + _length[e] - _potential[v];
 		                if (nd < heap[v]) {
-		                  heap.decrease(v, nd);
+		                  dn = d + _length[e] - _pi[v];
 		                  if (dn < heap[v]) {
 		                    heap.decrease(v, dn);
 		                  _pred[v] = e;
+		                }
 		                break;
@@ -184,13 +226,13 @@
 		              v = _graph.source(e);
 		              switch(heap.state(v)) {
 		              case Heap::PRE_HEAP:
-		                heap.push(v, d - _length[e] - _potential[v]);
+		                  heap.push(v, d - _length[e] - _pi[v]);
 		                _pred[v] = e;
 		                break;
 		              case Heap::IN_HEAP:
 		                nd = d - _length[e] - _potential[v];
 		                if (nd < heap[v]) {
-		                  heap.decrease(v, nd);
+		                  dn = d - _length[e] - _pi[v];
 		                  if (dn < heap[v]) {
 		                    heap.decrease(v, dn);
 		                  _pred[v] = e;
+		                }
 		                break;
@@ -205,7 +247,7 @@
 		        // Update potentials of processed nodes
 		        Length t_dist = heap.prio();
 		        for (int i = 0; i < int(_proc_nodes.size()); ++i)
-		          _potential[_proc_nodes[i]] += _dist[_proc_nodes[i]] - t_dist;
+		          _pi[_proc_nodes[i]] += _dist[_proc_nodes[i]] - t_dist;
 		        return true;
+		      }
@@ -226,19 +268,16 @@
 		    bool _local_potential;
 		    // The source node
-		    Node _source;
+		    Node _s;
 		    // The target node
-		    Node _target;
+		    Node _t;
 		    // Container to store the found paths
-		    std::vector< SimplePath<Digraph> > paths;
+		    std::vector<Path> _paths;
 		    int _path_num;
 		    // The pred arc map
 		    PredMap _pred;
 		    // Implementation of the Dijkstra algorithm for finding augmenting
 		    // shortest paths in the residual network
 		    ResidualDijkstra *_dijkstra;
 		  public:
@@ -258,7 +297,6 @@
 		    ~Suurballe() {
 		      if (_local_flow) delete _flow;
 		      if (_local_potential) delete _potential;
 		      delete _dijkstra;
+		    }
 		    /// \brief Set the flow map.
@@ -342,7 +380,7 @@
 		    ///
 		    /// \param s The source node.
 		    void init(const Node& s) {
-		      _source = s;
+		      _s = s;
 		      // Initialize maps
 		      if (!_flow) {
@@ -372,20 +410,18 @@
 		    ///
 		    /// \pre \ref init() must be called before using this function.
 		    int findFlow(const Node& t, int k = 2) {
 		      _target = t;
 		      _dijkstra =
 		        new ResidualDijkstra( _graph, *_flow, _length, *_potential, _pred,
 		                              _source, _target );
 		      _t = t;
 		      ResidualDijkstra dijkstra(*this);
 		      // Find shortest paths
 		      _path_num = 0;
 		      while (_path_num < k) {
 		        // Run Dijkstra
-		        if (!_dijkstra->run()) break;
+		        if (!dijkstra.run(_path_num)) break;
 		        ++_path_num;
 		        // Set the flow along the found shortest path
-		        Node u = _target;
+		        Node u = _t;
 		        Arc e;
 		        while ((e = _pred[u]) != INVALID) {
 		          if (u == _graph.target(e)) {
@@ -402,8 +438,8 @@
 		    /// \brief Compute the paths from the flow.
 		    ///
 		    /// This function computes the paths from the found minimum cost flow,
 		    /// which is the union of some arc-disjoint paths.
 		    /// This function computes arc-disjoint paths from the found minimum
 		    /// cost flow, which is the union of them.
 		    ///
 		    /// \pre \ref init() and \ref findFlow() must be called before using
 		    /// this function.
@@ -411,15 +447,15 @@
 		      FlowMap res_flow(_graph);
 		      for(ArcIt a(_graph); a != INVALID; ++a) res_flow[a] = (*_flow)[a];
 		      paths.clear();
 		      paths.resize(_path_num);
 		      _paths.clear();
 		      _paths.resize(_path_num);
 		      for (int i = 0; i < _path_num; ++i) {
 		        Node n = _source;
 		        while (n != _target) {
 		        Node n = _s;
 		        while (n != _t) {
 		          OutArcIt e(_graph, n);
 		          for ( ; res_flow[e] == 0; ++e) ;
 		          n = _graph.target(e);
-		          paths[i].addBack(e);
+		          _paths[i].addBack(e);
 		          res_flow[e] = 0;
+		        }
+		      }
@@ -518,7 +554,7 @@
 		    /// \pre \ref run() or \ref findPaths() must be called before using
 		    /// this function.
 		    const Path& path(int i) const {
-		      return paths[i];
+		      return _paths[i];
+		    }
 		    /// @}

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