# HG changeset patch
# User Peter Kovacs <kpeter@inf.elte.hu>
# Date 2009-11-12 23:29:42
# Node ID 9c428bb2b1056da486089cbcf6eee0c8e8ae4488
# Parent  78071e00de00622617c241ef612f6ba55ac2450d

Port CostScaling from SVN -r3524 (#180)

diff --git a/lemon/Makefile.am b/lemon/Makefile.am
--- a/lemon/Makefile.am
+++ b/lemon/Makefile.am
@@ -69,8 +69,9 @@
 	lemon/color.h \
 	lemon/concept_check.h \
 	lemon/connectivity.h \
+	lemon/core.h \
+	lemon/cost_scaling.h \
 	lemon/counter.h \
-	lemon/core.h \
 	lemon/cplex.h \
 	lemon/dfs.h \
 	lemon/dijkstra.h \
diff --git a/lemon/cost_scaling.h b/lemon/cost_scaling.h
new file mode 100644
--- /dev/null
+++ b/lemon/cost_scaling.h
@@ -0,0 +1,850 @@
+/* -*- C++ -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2003-2008
+ * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
+ * (Egervary Research Group on Combinatorial Optimization, EGRES).
+ *
+ * Permission to use, modify and distribute this software is granted
+ * provided that this copyright notice appears in all copies. For
+ * precise terms see the accompanying LICENSE file.
+ *
+ * This software is provided "AS IS" with no warranty of any kind,
+ * express or implied, and with no claim as to its suitability for any
+ * purpose.
+ *
+ */
+
+#ifndef LEMON_COST_SCALING_H
+#define LEMON_COST_SCALING_H
+
+/// \ingroup min_cost_flow_algs
+/// \file
+/// \brief Cost scaling algorithm for finding a minimum cost flow.
+
+#include <vector>
+#include <deque>
+#include <limits>
+
+#include <lemon/core.h>
+#include <lemon/maps.h>
+#include <lemon/math.h>
+#include <lemon/adaptors.h>
+#include <lemon/circulation.h>
+#include <lemon/bellman_ford.h>
+
+namespace lemon {
+
+  /// \addtogroup min_cost_flow_algs
+  /// @{
+
+  /// \brief Implementation of the cost scaling algorithm for finding a
+  /// minimum cost flow.
+  ///
+  /// \ref CostScaling implements the cost scaling algorithm performing
+  /// augment/push and relabel operations for finding a minimum cost
+  /// flow.
+  ///
+  /// \tparam Digraph The digraph type the algorithm runs on.
+  /// \tparam LowerMap The type of the lower bound map.
+  /// \tparam CapacityMap The type of the capacity (upper bound) map.
+  /// \tparam CostMap The type of the cost (length) map.
+  /// \tparam SupplyMap The type of the supply map.
+  ///
+  /// \warning
+  /// - Arc capacities and costs should be \e non-negative \e integers.
+  /// - Supply values should be \e signed \e integers.
+  /// - The value types of the maps should be convertible to each other.
+  /// - \c CostMap::Value must be signed type.
+  ///
+  /// \note Arc costs are multiplied with the number of nodes during
+  /// the algorithm so overflow problems may arise more easily than with
+  /// other minimum cost flow algorithms.
+  /// If it is available, <tt>long long int</tt> type is used instead of
+  /// <tt>long int</tt> in the inside computations.
+  ///
+  /// \author Peter Kovacs
+  template < typename Digraph,
+             typename LowerMap = typename Digraph::template ArcMap<int>,
+             typename CapacityMap = typename Digraph::template ArcMap<int>,
+             typename CostMap = typename Digraph::template ArcMap<int>,
+             typename SupplyMap = typename Digraph::template NodeMap<int> >
+  class CostScaling
+  {
+    TEMPLATE_DIGRAPH_TYPEDEFS(Digraph);
+
+    typedef typename CapacityMap::Value Capacity;
+    typedef typename CostMap::Value Cost;
+    typedef typename SupplyMap::Value Supply;
+    typedef typename Digraph::template ArcMap<Capacity> CapacityArcMap;
+    typedef typename Digraph::template NodeMap<Supply> SupplyNodeMap;
+
+    typedef ResidualDigraph< const Digraph,
+                             CapacityArcMap, CapacityArcMap > ResDigraph;
+    typedef typename ResDigraph::Arc ResArc;
+
+#if defined __GNUC__ && !defined __STRICT_ANSI__
+    typedef long long int LCost;
+#else
+    typedef long int LCost;
+#endif
+    typedef typename Digraph::template ArcMap<LCost> LargeCostMap;
+
+  public:
+
+    /// The type of the flow map.
+    typedef typename Digraph::template ArcMap<Capacity> FlowMap;
+    /// The type of the potential map.
+    typedef typename Digraph::template NodeMap<LCost> PotentialMap;
+
+  private:
+
+    /// \brief Map adaptor class for handling residual arc costs.
+    ///
+    /// Map adaptor class for handling residual arc costs.
+    template <typename Map>
+    class ResidualCostMap : public MapBase<ResArc, typename Map::Value>
+    {
+    private:
+
+      const Map &_cost_map;
+
+    public:
+
+      ///\e
+      ResidualCostMap(const Map &cost_map) :
+        _cost_map(cost_map) {}
+
+      ///\e
+      inline typename Map::Value operator[](const ResArc &e) const {
+        return ResDigraph::forward(e) ? _cost_map[e] : -_cost_map[e];
+      }
+
+    }; //class ResidualCostMap
+
+    /// \brief Map adaptor class for handling reduced arc costs.
+    ///
+    /// Map adaptor class for handling reduced arc costs.
+    class ReducedCostMap : public MapBase<Arc, LCost>
+    {
+    private:
+
+      const Digraph &_gr;
+      const LargeCostMap &_cost_map;
+      const PotentialMap &_pot_map;
+
+    public:
+
+      ///\e
+      ReducedCostMap( const Digraph &gr,
+                      const LargeCostMap &cost_map,
+                      const PotentialMap &pot_map ) :
+        _gr(gr), _cost_map(cost_map), _pot_map(pot_map) {}
+
+      ///\e
+      inline LCost operator[](const Arc &e) const {
+        return _cost_map[e] + _pot_map[_gr.source(e)]
+                            - _pot_map[_gr.target(e)];
+      }
+
+    }; //class ReducedCostMap
+
+  private:
+
+    // The digraph the algorithm runs on
+    const Digraph &_graph;
+    // The original lower bound map
+    const LowerMap *_lower;
+    // The modified capacity map
+    CapacityArcMap _capacity;
+    // The original cost map
+    const CostMap &_orig_cost;
+    // The scaled cost map
+    LargeCostMap _cost;
+    // The modified supply map
+    SupplyNodeMap _supply;
+    bool _valid_supply;
+
+    // Arc map of the current flow
+    FlowMap *_flow;
+    bool _local_flow;
+    // Node map of the current potentials
+    PotentialMap *_potential;
+    bool _local_potential;
+
+    // The residual cost map
+    ResidualCostMap<LargeCostMap> _res_cost;
+    // The residual digraph
+    ResDigraph *_res_graph;
+    // The reduced cost map
+    ReducedCostMap *_red_cost;
+    // The excess map
+    SupplyNodeMap _excess;
+    // The epsilon parameter used for cost scaling
+    LCost _epsilon;
+    // The scaling factor
+    int _alpha;
+
+  public:
+
+    /// \brief General constructor (with lower bounds).
+    ///
+    /// General constructor (with lower bounds).
+    ///
+    /// \param digraph The digraph the algorithm runs on.
+    /// \param lower The lower bounds of the arcs.
+    /// \param capacity The capacities (upper bounds) of the arcs.
+    /// \param cost The cost (length) values of the arcs.
+    /// \param supply The supply values of the nodes (signed).
+    CostScaling( const Digraph &digraph,
+                 const LowerMap &lower,
+                 const CapacityMap &capacity,
+                 const CostMap &cost,
+                 const SupplyMap &supply ) :
+      _graph(digraph), _lower(&lower), _capacity(digraph), _orig_cost(cost),
+      _cost(digraph), _supply(digraph), _flow(NULL), _local_flow(false),
+      _potential(NULL), _local_potential(false), _res_cost(_cost),
+      _res_graph(NULL), _red_cost(NULL), _excess(digraph, 0)
+    {
+      // Check the sum of supply values
+      Supply sum = 0;
+      for (NodeIt n(_graph); n != INVALID; ++n) sum += _supply[n];
+      _valid_supply = sum == 0;
+      
+      for (ArcIt e(_graph); e != INVALID; ++e) _capacity[e] = capacity[e];
+      for (NodeIt n(_graph); n != INVALID; ++n) _supply[n] = supply[n];
+
+      // Remove non-zero lower bounds
+      for (ArcIt e(_graph); e != INVALID; ++e) {
+        if (lower[e] != 0) {
+          _capacity[e] -= lower[e];
+          _supply[_graph.source(e)] -= lower[e];
+          _supply[_graph.target(e)] += lower[e];
+        }
+      }
+    }
+/*
+    /// \brief General constructor (without lower bounds).
+    ///
+    /// General constructor (without lower bounds).
+    ///
+    /// \param digraph The digraph the algorithm runs on.
+    /// \param capacity The capacities (upper bounds) of the arcs.
+    /// \param cost The cost (length) values of the arcs.
+    /// \param supply The supply values of the nodes (signed).
+    CostScaling( const Digraph &digraph,
+                 const CapacityMap &capacity,
+                 const CostMap &cost,
+                 const SupplyMap &supply ) :
+      _graph(digraph), _lower(NULL), _capacity(capacity), _orig_cost(cost),
+      _cost(digraph), _supply(supply), _flow(NULL), _local_flow(false),
+      _potential(NULL), _local_potential(false), _res_cost(_cost),
+      _res_graph(NULL), _red_cost(NULL), _excess(digraph, 0)
+    {
+      // Check the sum of supply values
+      Supply sum = 0;
+      for (NodeIt n(_graph); n != INVALID; ++n) sum += _supply[n];
+      _valid_supply = sum == 0;
+    }
+
+    /// \brief Simple constructor (with lower bounds).
+    ///
+    /// Simple constructor (with lower bounds).
+    ///
+    /// \param digraph The digraph the algorithm runs on.
+    /// \param lower The lower bounds of the arcs.
+    /// \param capacity The capacities (upper bounds) of the arcs.
+    /// \param cost The cost (length) values of the arcs.
+    /// \param s The source node.
+    /// \param t The target node.
+    /// \param flow_value The required amount of flow from node \c s
+    /// to node \c t (i.e. the supply of \c s and the demand of \c t).
+    CostScaling( const Digraph &digraph,
+                 const LowerMap &lower,
+                 const CapacityMap &capacity,
+                 const CostMap &cost,
+                 Node s, Node t,
+                 Supply flow_value ) :
+      _graph(digraph), _lower(&lower), _capacity(capacity), _orig_cost(cost),
+      _cost(digraph), _supply(digraph, 0), _flow(NULL), _local_flow(false),
+      _potential(NULL), _local_potential(false), _res_cost(_cost),
+      _res_graph(NULL), _red_cost(NULL), _excess(digraph, 0)
+    {
+      // Remove non-zero lower bounds
+      _supply[s] =  flow_value;
+      _supply[t] = -flow_value;
+      for (ArcIt e(_graph); e != INVALID; ++e) {
+        if (lower[e] != 0) {
+          _capacity[e] -= lower[e];
+          _supply[_graph.source(e)] -= lower[e];
+          _supply[_graph.target(e)] += lower[e];
+        }
+      }
+      _valid_supply = true;
+    }
+
+    /// \brief Simple constructor (without lower bounds).
+    ///
+    /// Simple constructor (without lower bounds).
+    ///
+    /// \param digraph The digraph the algorithm runs on.
+    /// \param capacity The capacities (upper bounds) of the arcs.
+    /// \param cost The cost (length) values of the arcs.
+    /// \param s The source node.
+    /// \param t The target node.
+    /// \param flow_value The required amount of flow from node \c s
+    /// to node \c t (i.e. the supply of \c s and the demand of \c t).
+    CostScaling( const Digraph &digraph,
+                 const CapacityMap &capacity,
+                 const CostMap &cost,
+                 Node s, Node t,
+                 Supply flow_value ) :
+      _graph(digraph), _lower(NULL), _capacity(capacity), _orig_cost(cost),
+      _cost(digraph), _supply(digraph, 0), _flow(NULL), _local_flow(false),
+      _potential(NULL), _local_potential(false), _res_cost(_cost),
+      _res_graph(NULL), _red_cost(NULL), _excess(digraph, 0)
+    {
+      _supply[s] =  flow_value;
+      _supply[t] = -flow_value;
+      _valid_supply = true;
+    }
+*/
+    /// Destructor.
+    ~CostScaling() {
+      if (_local_flow) delete _flow;
+      if (_local_potential) delete _potential;
+      delete _res_graph;
+      delete _red_cost;
+    }
+
+    /// \brief Set the flow map.
+    ///
+    /// Set the flow map.
+    ///
+    /// \return \c (*this)
+    CostScaling& flowMap(FlowMap &map) {
+      if (_local_flow) {
+        delete _flow;
+        _local_flow = false;
+      }
+      _flow = &map;
+      return *this;
+    }
+
+    /// \brief Set the potential map.
+    ///
+    /// Set the potential map.
+    ///
+    /// \return \c (*this)
+    CostScaling& potentialMap(PotentialMap &map) {
+      if (_local_potential) {
+        delete _potential;
+        _local_potential = false;
+      }
+      _potential = &map;
+      return *this;
+    }
+
+    /// \name Execution control
+
+    /// @{
+
+    /// \brief Run the algorithm.
+    ///
+    /// Run the algorithm.
+    ///
+    /// \param partial_augment By default the algorithm performs
+    /// partial augment and relabel operations in the cost scaling
+    /// phases. Set this parameter to \c false for using local push and
+    /// relabel operations instead.
+    ///
+    /// \return \c true if a feasible flow can be found.
+    bool run(bool partial_augment = true) {
+      if (partial_augment) {
+        return init() && startPartialAugment();
+      } else {
+        return init() && startPushRelabel();
+      }
+    }
+
+    /// @}
+
+    /// \name Query Functions
+    /// The result of the algorithm can be obtained using these
+    /// functions.\n
+    /// \ref lemon::CostScaling::run() "run()" must be called before
+    /// using them.
+
+    /// @{
+
+    /// \brief Return a const reference to the arc map storing the
+    /// found flow.
+    ///
+    /// Return a const reference to the arc map storing the found flow.
+    ///
+    /// \pre \ref run() must be called before using this function.
+    const FlowMap& flowMap() const {
+      return *_flow;
+    }
+
+    /// \brief Return a const reference to the node map storing the
+    /// found potentials (the dual solution).
+    ///
+    /// Return a const reference to the node map storing the found
+    /// potentials (the dual solution).
+    ///
+    /// \pre \ref run() must be called before using this function.
+    const PotentialMap& potentialMap() const {
+      return *_potential;
+    }
+
+    /// \brief Return the flow on the given arc.
+    ///
+    /// Return the flow on the given arc.
+    ///
+    /// \pre \ref run() must be called before using this function.
+    Capacity flow(const Arc& arc) const {
+      return (*_flow)[arc];
+    }
+
+    /// \brief Return the potential of the given node.
+    ///
+    /// Return the potential of the given node.
+    ///
+    /// \pre \ref run() must be called before using this function.
+    Cost potential(const Node& node) const {
+      return (*_potential)[node];
+    }
+
+    /// \brief Return the total cost of the found flow.
+    ///
+    /// Return the total cost of the found flow. The complexity of the
+    /// function is \f$ O(e) \f$.
+    ///
+    /// \pre \ref run() must be called before using this function.
+    Cost totalCost() const {
+      Cost c = 0;
+      for (ArcIt e(_graph); e != INVALID; ++e)
+        c += (*_flow)[e] * _orig_cost[e];
+      return c;
+    }
+
+    /// @}
+
+  private:
+
+    /// Initialize the algorithm.
+    bool init() {
+      if (!_valid_supply) return false;
+      // The scaling factor
+      _alpha = 8;
+
+      // Initialize flow and potential maps
+      if (!_flow) {
+        _flow = new FlowMap(_graph);
+        _local_flow = true;
+      }
+      if (!_potential) {
+        _potential = new PotentialMap(_graph);
+        _local_potential = true;
+      }
+
+      _red_cost = new ReducedCostMap(_graph, _cost, *_potential);
+      _res_graph = new ResDigraph(_graph, _capacity, *_flow);
+
+      // Initialize the scaled cost map and the epsilon parameter
+      Cost max_cost = 0;
+      int node_num = countNodes(_graph);
+      for (ArcIt e(_graph); e != INVALID; ++e) {
+        _cost[e] = LCost(_orig_cost[e]) * node_num * _alpha;
+        if (_orig_cost[e] > max_cost) max_cost = _orig_cost[e];
+      }
+      _epsilon = max_cost * node_num;
+
+      // Find a feasible flow using Circulation
+      Circulation< Digraph, ConstMap<Arc, Capacity>, CapacityArcMap,
+                   SupplyMap >
+        circulation( _graph, constMap<Arc>(Capacity(0)), _capacity,
+                     _supply );
+      return circulation.flowMap(*_flow).run();
+    }
+
+    /// Execute the algorithm performing partial augmentation and
+    /// relabel operations.
+    bool startPartialAugment() {
+      // Paramters for heuristics
+//      const int BF_HEURISTIC_EPSILON_BOUND = 1000;
+//      const int BF_HEURISTIC_BOUND_FACTOR  = 3;
+      // Maximum augment path length
+      const int MAX_PATH_LENGTH = 4;
+
+      // Variables
+      typename Digraph::template NodeMap<Arc> pred_arc(_graph);
+      typename Digraph::template NodeMap<bool> forward(_graph);
+      typename Digraph::template NodeMap<OutArcIt> next_out(_graph);
+      typename Digraph::template NodeMap<InArcIt> next_in(_graph);
+      typename Digraph::template NodeMap<bool> next_dir(_graph);
+      std::deque<Node> active_nodes;
+      std::vector<Node> path_nodes;
+
+//      int node_num = countNodes(_graph);
+      for ( ; _epsilon >= 1; _epsilon = _epsilon < _alpha && _epsilon > 1 ?
+                                        1 : _epsilon / _alpha )
+      {
+/*
+        // "Early Termination" heuristic: use Bellman-Ford algorithm
+        // to check if the current flow is optimal
+        if (_epsilon <= BF_HEURISTIC_EPSILON_BOUND) {
+          typedef ShiftMap< ResidualCostMap<LargeCostMap> > ShiftCostMap;
+          ShiftCostMap shift_cost(_res_cost, 1);
+          BellmanFord<ResDigraph, ShiftCostMap> bf(*_res_graph, shift_cost);
+          bf.init(0);
+          bool done = false;
+          int K = int(BF_HEURISTIC_BOUND_FACTOR * sqrt(node_num));
+          for (int i = 0; i < K && !done; ++i)
+            done = bf.processNextWeakRound();
+          if (done) break;
+        }
+*/
+        // Saturate arcs not satisfying the optimality condition
+        Capacity delta;
+        for (ArcIt e(_graph); e != INVALID; ++e) {
+          if (_capacity[e] - (*_flow)[e] > 0 && (*_red_cost)[e] < 0) {
+            delta = _capacity[e] - (*_flow)[e];
+            _excess[_graph.source(e)] -= delta;
+            _excess[_graph.target(e)] += delta;
+            (*_flow)[e] = _capacity[e];
+          }
+          if ((*_flow)[e] > 0 && -(*_red_cost)[e] < 0) {
+            _excess[_graph.target(e)] -= (*_flow)[e];
+            _excess[_graph.source(e)] += (*_flow)[e];
+            (*_flow)[e] = 0;
+          }
+        }
+
+        // Find active nodes (i.e. nodes with positive excess)
+        for (NodeIt n(_graph); n != INVALID; ++n) {
+          if (_excess[n] > 0) active_nodes.push_back(n);
+        }
+
+        // Initialize the next arc maps
+        for (NodeIt n(_graph); n != INVALID; ++n) {
+          next_out[n] = OutArcIt(_graph, n);
+          next_in[n] = InArcIt(_graph, n);
+          next_dir[n] = true;
+        }
+
+        // Perform partial augment and relabel operations
+        while (active_nodes.size() > 0) {
+          // Select an active node (FIFO selection)
+          if (_excess[active_nodes[0]] <= 0) {
+            active_nodes.pop_front();
+            continue;
+          }
+          Node start = active_nodes[0];
+          path_nodes.clear();
+          path_nodes.push_back(start);
+
+          // Find an augmenting path from the start node
+          Node u, tip = start;
+          LCost min_red_cost;
+          while ( _excess[tip] >= 0 &&
+                  int(path_nodes.size()) <= MAX_PATH_LENGTH )
+          {
+            if (next_dir[tip]) {
+              for (OutArcIt e = next_out[tip]; e != INVALID; ++e) {
+                if (_capacity[e] - (*_flow)[e] > 0 && (*_red_cost)[e] < 0) {
+                  u = _graph.target(e);
+                  pred_arc[u] = e;
+                  forward[u] = true;
+                  next_out[tip] = e;
+                  tip = u;
+                  path_nodes.push_back(tip);
+                  goto next_step;
+                }
+              }
+              next_dir[tip] = false;
+            }
+            for (InArcIt e = next_in[tip]; e != INVALID; ++e) {
+              if ((*_flow)[e] > 0 && -(*_red_cost)[e] < 0) {
+                u = _graph.source(e);
+                pred_arc[u] = e;
+                forward[u] = false;
+                next_in[tip] = e;
+                tip = u;
+                path_nodes.push_back(tip);
+                goto next_step;
+              }
+            }
+
+            // Relabel tip node
+            min_red_cost = std::numeric_limits<LCost>::max() / 2;
+            for (OutArcIt oe(_graph, tip); oe != INVALID; ++oe) {
+              if ( _capacity[oe] - (*_flow)[oe] > 0 &&
+                   (*_red_cost)[oe] < min_red_cost )
+                min_red_cost = (*_red_cost)[oe];
+            }
+            for (InArcIt ie(_graph, tip); ie != INVALID; ++ie) {
+              if ((*_flow)[ie] > 0 && -(*_red_cost)[ie] < min_red_cost)
+                min_red_cost = -(*_red_cost)[ie];
+            }
+            (*_potential)[tip] -= min_red_cost + _epsilon;
+
+            // Reset the next arc maps
+            next_out[tip] = OutArcIt(_graph, tip);
+            next_in[tip] = InArcIt(_graph, tip);
+            next_dir[tip] = true;
+
+            // Step back
+            if (tip != start) {
+              path_nodes.pop_back();
+              tip = path_nodes[path_nodes.size()-1];
+            }
+
+          next_step:
+            continue;
+          }
+
+          // Augment along the found path (as much flow as possible)
+          Capacity delta;
+          for (int i = 1; i < int(path_nodes.size()); ++i) {
+            u = path_nodes[i];
+            delta = forward[u] ?
+              _capacity[pred_arc[u]] - (*_flow)[pred_arc[u]] :
+              (*_flow)[pred_arc[u]];
+            delta = std::min(delta, _excess[path_nodes[i-1]]);
+            (*_flow)[pred_arc[u]] += forward[u] ? delta : -delta;
+            _excess[path_nodes[i-1]] -= delta;
+            _excess[u] += delta;
+            if (_excess[u] > 0 && _excess[u] <= delta) active_nodes.push_back(u);
+          }
+        }
+      }
+
+      // Compute node potentials for the original costs
+      ResidualCostMap<CostMap> res_cost(_orig_cost);
+      BellmanFord< ResDigraph, ResidualCostMap<CostMap> >
+        bf(*_res_graph, res_cost);
+      bf.init(0); bf.start();
+      for (NodeIt n(_graph); n != INVALID; ++n)
+        (*_potential)[n] = bf.dist(n);
+
+      // Handle non-zero lower bounds
+      if (_lower) {
+        for (ArcIt e(_graph); e != INVALID; ++e)
+          (*_flow)[e] += (*_lower)[e];
+      }
+      return true;
+    }
+
+    /// Execute the algorithm performing push and relabel operations.
+    bool startPushRelabel() {
+      // Paramters for heuristics
+//      const int BF_HEURISTIC_EPSILON_BOUND = 1000;
+//      const int BF_HEURISTIC_BOUND_FACTOR  = 3;
+
+      typename Digraph::template NodeMap<bool> hyper(_graph, false);
+      typename Digraph::template NodeMap<Arc> pred_arc(_graph);
+      typename Digraph::template NodeMap<bool> forward(_graph);
+      typename Digraph::template NodeMap<OutArcIt> next_out(_graph);
+      typename Digraph::template NodeMap<InArcIt> next_in(_graph);
+      typename Digraph::template NodeMap<bool> next_dir(_graph);
+      std::deque<Node> active_nodes;
+
+//      int node_num = countNodes(_graph);
+      for ( ; _epsilon >= 1; _epsilon = _epsilon < _alpha && _epsilon > 1 ?
+                                        1 : _epsilon / _alpha )
+      {
+/*
+        // "Early Termination" heuristic: use Bellman-Ford algorithm
+        // to check if the current flow is optimal
+        if (_epsilon <= BF_HEURISTIC_EPSILON_BOUND) {
+          typedef ShiftMap< ResidualCostMap<LargeCostMap> > ShiftCostMap;
+          ShiftCostMap shift_cost(_res_cost, 1);
+          BellmanFord<ResDigraph, ShiftCostMap> bf(*_res_graph, shift_cost);
+          bf.init(0);
+          bool done = false;
+          int K = int(BF_HEURISTIC_BOUND_FACTOR * sqrt(node_num));
+          for (int i = 0; i < K && !done; ++i)
+            done = bf.processNextWeakRound();
+          if (done) break;
+        }
+*/
+
+        // Saturate arcs not satisfying the optimality condition
+        Capacity delta;
+        for (ArcIt e(_graph); e != INVALID; ++e) {
+          if (_capacity[e] - (*_flow)[e] > 0 && (*_red_cost)[e] < 0) {
+            delta = _capacity[e] - (*_flow)[e];
+            _excess[_graph.source(e)] -= delta;
+            _excess[_graph.target(e)] += delta;
+            (*_flow)[e] = _capacity[e];
+          }
+          if ((*_flow)[e] > 0 && -(*_red_cost)[e] < 0) {
+            _excess[_graph.target(e)] -= (*_flow)[e];
+            _excess[_graph.source(e)] += (*_flow)[e];
+            (*_flow)[e] = 0;
+          }
+        }
+
+        // Find active nodes (i.e. nodes with positive excess)
+        for (NodeIt n(_graph); n != INVALID; ++n) {
+          if (_excess[n] > 0) active_nodes.push_back(n);
+        }
+
+        // Initialize the next arc maps
+        for (NodeIt n(_graph); n != INVALID; ++n) {
+          next_out[n] = OutArcIt(_graph, n);
+          next_in[n] = InArcIt(_graph, n);
+          next_dir[n] = true;
+        }
+
+        // Perform push and relabel operations
+        while (active_nodes.size() > 0) {
+          // Select an active node (FIFO selection)
+          Node n = active_nodes[0], t;
+          bool relabel_enabled = true;
+
+          // Perform push operations if there are admissible arcs
+          if (_excess[n] > 0 && next_dir[n]) {
+            OutArcIt e = next_out[n];
+            for ( ; e != INVALID; ++e) {
+              if (_capacity[e] - (*_flow)[e] > 0 && (*_red_cost)[e] < 0) {
+                delta = std::min(_capacity[e] - (*_flow)[e], _excess[n]);
+                t = _graph.target(e);
+
+                // Push-look-ahead heuristic
+                Capacity ahead = -_excess[t];
+                for (OutArcIt oe(_graph, t); oe != INVALID; ++oe) {
+                  if (_capacity[oe] - (*_flow)[oe] > 0 && (*_red_cost)[oe] < 0)
+                    ahead += _capacity[oe] - (*_flow)[oe];
+                }
+                for (InArcIt ie(_graph, t); ie != INVALID; ++ie) {
+                  if ((*_flow)[ie] > 0 && -(*_red_cost)[ie] < 0)
+                    ahead += (*_flow)[ie];
+                }
+                if (ahead < 0) ahead = 0;
+
+                // Push flow along the arc
+                if (ahead < delta) {
+                  (*_flow)[e] += ahead;
+                  _excess[n] -= ahead;
+                  _excess[t] += ahead;
+                  active_nodes.push_front(t);
+                  hyper[t] = true;
+                  relabel_enabled = false;
+                  break;
+                } else {
+                  (*_flow)[e] += delta;
+                  _excess[n] -= delta;
+                  _excess[t] += delta;
+                  if (_excess[t] > 0 && _excess[t] <= delta)
+                    active_nodes.push_back(t);
+                }
+
+                if (_excess[n] == 0) break;
+              }
+            }
+            if (e != INVALID) {
+              next_out[n] = e;
+            } else {
+              next_dir[n] = false;
+            }
+          }
+
+          if (_excess[n] > 0 && !next_dir[n]) {
+            InArcIt e = next_in[n];
+            for ( ; e != INVALID; ++e) {
+              if ((*_flow)[e] > 0 && -(*_red_cost)[e] < 0) {
+                delta = std::min((*_flow)[e], _excess[n]);
+                t = _graph.source(e);
+
+                // Push-look-ahead heuristic
+                Capacity ahead = -_excess[t];
+                for (OutArcIt oe(_graph, t); oe != INVALID; ++oe) {
+                  if (_capacity[oe] - (*_flow)[oe] > 0 && (*_red_cost)[oe] < 0)
+                    ahead += _capacity[oe] - (*_flow)[oe];
+                }
+                for (InArcIt ie(_graph, t); ie != INVALID; ++ie) {
+                  if ((*_flow)[ie] > 0 && -(*_red_cost)[ie] < 0)
+                    ahead += (*_flow)[ie];
+                }
+                if (ahead < 0) ahead = 0;
+
+                // Push flow along the arc
+                if (ahead < delta) {
+                  (*_flow)[e] -= ahead;
+                  _excess[n] -= ahead;
+                  _excess[t] += ahead;
+                  active_nodes.push_front(t);
+                  hyper[t] = true;
+                  relabel_enabled = false;
+                  break;
+                } else {
+                  (*_flow)[e] -= delta;
+                  _excess[n] -= delta;
+                  _excess[t] += delta;
+                  if (_excess[t] > 0 && _excess[t] <= delta)
+                    active_nodes.push_back(t);
+                }
+
+                if (_excess[n] == 0) break;
+              }
+            }
+            next_in[n] = e;
+          }
+
+          // Relabel the node if it is still active (or hyper)
+          if (relabel_enabled && (_excess[n] > 0 || hyper[n])) {
+            LCost min_red_cost = std::numeric_limits<LCost>::max() / 2;
+            for (OutArcIt oe(_graph, n); oe != INVALID; ++oe) {
+              if ( _capacity[oe] - (*_flow)[oe] > 0 &&
+                   (*_red_cost)[oe] < min_red_cost )
+                min_red_cost = (*_red_cost)[oe];
+            }
+            for (InArcIt ie(_graph, n); ie != INVALID; ++ie) {
+              if ((*_flow)[ie] > 0 && -(*_red_cost)[ie] < min_red_cost)
+                min_red_cost = -(*_red_cost)[ie];
+            }
+            (*_potential)[n] -= min_red_cost + _epsilon;
+            hyper[n] = false;
+
+            // Reset the next arc maps
+            next_out[n] = OutArcIt(_graph, n);
+            next_in[n] = InArcIt(_graph, n);
+            next_dir[n] = true;
+          }
+
+          // Remove nodes that are not active nor hyper
+          while ( active_nodes.size() > 0 &&
+                  _excess[active_nodes[0]] <= 0 &&
+                  !hyper[active_nodes[0]] ) {
+            active_nodes.pop_front();
+          }
+        }
+      }
+
+      // Compute node potentials for the original costs
+      ResidualCostMap<CostMap> res_cost(_orig_cost);
+      BellmanFord< ResDigraph, ResidualCostMap<CostMap> >
+        bf(*_res_graph, res_cost);
+      bf.init(0); bf.start();
+      for (NodeIt n(_graph); n != INVALID; ++n)
+        (*_potential)[n] = bf.dist(n);
+
+      // Handle non-zero lower bounds
+      if (_lower) {
+        for (ArcIt e(_graph); e != INVALID; ++e)
+          (*_flow)[e] += (*_lower)[e];
+      }
+      return true;
+    }
+
+  }; //class CostScaling
+
+  ///@}
+
+} //namespace lemon
+
+#endif //LEMON_COST_SCALING_H