source: lemon-0.x/lemon/capacity_scaling.h @ 2507:6520edb2c3f3

/* -*- C++ -*-
 *
 * This file is a part of LEMON, a generic C++ optimization library
 *
 * Copyright (C) 2003-2007
 * 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_CAPACITY_SCALING_H
#define LEMON_CAPACITY_SCALING_H

/// \ingroup min_cost_flow
///
/// \file
/// \brief The capacity scaling algorithm for finding a minimum cost
/// flow.

#include <vector>
#include <lemon/dijkstra.h>
#include <lemon/graph_adaptor.h>

#define WITH_SCALING

#ifdef WITH_SCALING
#define SCALING_FACTOR    2
#endif

//#define _DEBUG_ITER_

namespace lemon {

  /// \addtogroup min_cost_flow
  /// @{

  /// \brief Implementation of the capacity scaling version of the
  /// successive shortest path algorithm for finding a minimum cost flow.
  ///
  /// \ref lemon::CapacityScaling "CapacityScaling" implements a
  /// capacity scaling algorithm for finding a minimum cost flow.
  ///
  /// \param Graph The directed graph type the algorithm runs on.
  /// \param LowerMap The type of the lower bound map.
  /// \param CapacityMap The type of the capacity (upper bound) map.
  /// \param CostMap The type of the cost (length) map.
  /// \param SupplyMap The type of the supply map.
  ///
  /// \warning
  /// - Edge capacities and costs should be nonnegative integers.
  ///   However \c CostMap::Value should be signed type.
  /// - Supply values should be integers.
  /// - \c LowerMap::Value must be convertible to
  ///   \c CapacityMap::Value and \c CapacityMap::Value must be
  ///   convertible to \c SupplyMap::Value.
  ///
  /// \author Peter Kovacs

template < typename Graph,
           typename LowerMap = typename Graph::template EdgeMap<int>,
           typename CapacityMap = LowerMap,
           typename CostMap = typename Graph::template EdgeMap<int>,
           typename SupplyMap = typename Graph::template NodeMap
                                <typename CapacityMap::Value> >
  class CapacityScaling
  {
    typedef typename Graph::Node Node;
    typedef typename Graph::NodeIt NodeIt;
    typedef typename Graph::Edge Edge;
    typedef typename Graph::EdgeIt EdgeIt;
    typedef typename Graph::InEdgeIt InEdgeIt;
    typedef typename Graph::OutEdgeIt OutEdgeIt;

    typedef typename LowerMap::Value Lower;
    typedef typename CapacityMap::Value Capacity;
    typedef typename CostMap::Value Cost;
    typedef typename SupplyMap::Value Supply;
    typedef typename Graph::template EdgeMap<Capacity> CapacityRefMap;
    typedef typename Graph::template NodeMap<Supply> SupplyRefMap;

    typedef ResGraphAdaptor< const Graph, Capacity,
                             CapacityRefMap, CapacityRefMap > ResGraph;
    typedef typename ResGraph::Node ResNode;
    typedef typename ResGraph::NodeIt ResNodeIt;
    typedef typename ResGraph::Edge ResEdge;
    typedef typename ResGraph::EdgeIt ResEdgeIt;

  public:

    /// \brief The type of the flow map.
    typedef CapacityRefMap FlowMap;
    /// \brief The type of the potential map.
    typedef typename Graph::template NodeMap<Cost> PotentialMap;

  protected:

    /// \brief Map adaptor class for handling reduced edge costs.
    class ReducedCostMap : public MapBase<ResEdge, Cost>
    {
    private:

      const ResGraph &gr;
      const CostMap &cost_map;
      const PotentialMap &pot_map;

    public:

      typedef typename MapBase<ResEdge, Cost>::Value Value;
      typedef typename MapBase<ResEdge, Cost>::Key Key;

      ReducedCostMap( const ResGraph &_gr,
                      const CostMap &_cost,
                      const PotentialMap &_pot ) :
        gr(_gr), cost_map(_cost), pot_map(_pot) {}

      Value operator[](const Key &e) const {
        return ResGraph::forward(e) ?
           cost_map[e] - pot_map[gr.source(e)] + pot_map[gr.target(e)] :
          -cost_map[e] - pot_map[gr.source(e)] + pot_map[gr.target(e)];
      }

    }; //class ReducedCostMap

    /// \brief Map adaptor for \ref lemon::Dijkstra "Dijkstra" class to
    /// update node potentials.
    class PotentialUpdateMap : public MapBase<ResNode, Cost>
    {
    private:

      PotentialMap *pot;
      typedef std::pair<ResNode, Cost> Pair;
      std::vector<Pair> data;

    public:

      typedef typename MapBase<ResNode, Cost>::Value Value;
      typedef typename MapBase<ResNode, Cost>::Key Key;

      void potentialMap(PotentialMap &_pot) {
        pot = &_pot;
      }

      void init() {
        data.clear();
      }

      void set(const Key &n, const Value &v) {
        data.push_back(Pair(n, v));
      }

      void update() {
        Cost val = data[data.size()-1].second;
        for (int i = 0; i < data.size()-1; ++i)
          (*pot)[data[i].first] += val - data[i].second;
      }

    }; //class PotentialUpdateMap

#ifdef WITH_SCALING
    /// \brief Map adaptor class for identifing deficit nodes.
    class DeficitBoolMap : public MapBase<ResNode, bool>
    {
    private:

      const SupplyRefMap &imb;
      const Capacity &delta;

    public:

      DeficitBoolMap(const SupplyRefMap &_imb, const Capacity &_delta) :
        imb(_imb), delta(_delta) {}

      bool operator[](const ResNode &n) const {
        return imb[n] <= -delta;
      }

    }; //class DeficitBoolMap

    /// \brief Map adaptor class for filtering edges with at least
    /// \c delta residual capacity
    class DeltaFilterMap : public MapBase<ResEdge, bool>
    {
    private:

      const ResGraph &gr;
      const Capacity &delta;

    public:

      typedef typename MapBase<ResEdge, Cost>::Value Value;
      typedef typename MapBase<ResEdge, Cost>::Key Key;

      DeltaFilterMap(const ResGraph &_gr, const Capacity &_delta) :
        gr(_gr), delta(_delta) {}

      Value operator[](const Key &e) const {
        return gr.rescap(e) >= delta;
      }

    }; //class DeltaFilterMap

    typedef EdgeSubGraphAdaptor<const ResGraph, const DeltaFilterMap>
      DeltaResGraph;

    /// \brief Traits class for \ref lemon::Dijkstra "Dijkstra" class.
    class ResDijkstraTraits :
      public DijkstraDefaultTraits<DeltaResGraph, ReducedCostMap>
    {
    public:

      typedef PotentialUpdateMap DistMap;

      static DistMap *createDistMap(const DeltaResGraph&) {
        return new DistMap();
      }

    }; //class ResDijkstraTraits

#else //WITHOUT_CAPACITY_SCALING
    /// \brief Map adaptor class for identifing deficit nodes.
    class DeficitBoolMap : public MapBase<ResNode, bool>
    {
    private:

      const SupplyRefMap &imb;

    public:

      DeficitBoolMap(const SupplyRefMap &_imb) : imb(_imb) {}

      bool operator[](const ResNode &n) const {
        return imb[n] < 0;
      }

    }; //class DeficitBoolMap

    /// \brief Traits class for \ref lemon::Dijkstra "Dijkstra" class.
    class ResDijkstraTraits :
      public DijkstraDefaultTraits<ResGraph, ReducedCostMap>
    {
    public:

      typedef PotentialUpdateMap DistMap;

      static DistMap *createDistMap(const ResGraph&) {
        return new DistMap();
      }

    }; //class ResDijkstraTraits
#endif

  protected:

    /// \brief The directed graph the algorithm runs on.
    const Graph &graph;
    /// \brief The original lower bound map.
    const LowerMap *lower;
    /// \brief The modified capacity map.
    CapacityRefMap capacity;
    /// \brief The cost map.
    const CostMap &cost;
    /// \brief The modified supply map.
    SupplyRefMap supply;
    /// \brief The sum of supply values equals zero.
    bool valid_supply;

    /// \brief The edge map of the current flow.
    FlowMap flow;
    /// \brief The potential node map.
    PotentialMap potential;
    /// \brief The residual graph.
    ResGraph res_graph;
    /// \brief The reduced cost map.
    ReducedCostMap red_cost;

    /// \brief The imbalance map.
    SupplyRefMap imbalance;
    /// \brief The excess nodes.
    std::vector<ResNode> excess_nodes;
    /// \brief The index of the next excess node.
    int next_node;

#ifdef WITH_SCALING
    typedef Dijkstra<DeltaResGraph, ReducedCostMap, ResDijkstraTraits>
      ResDijkstra;
    /// \brief \ref lemon::Dijkstra "Dijkstra" class for finding
    /// shortest paths in the residual graph with respect to the
    /// reduced edge costs.
    ResDijkstra dijkstra;

    /// \brief The delta parameter used for capacity scaling.
    Capacity delta;
    /// \brief Edge filter map.
    DeltaFilterMap delta_filter;
    /// \brief The delta residual graph.
    DeltaResGraph dres_graph;
    /// \brief Map for identifing deficit nodes.
    DeficitBoolMap delta_deficit;

    /// \brief The deficit nodes.
    std::vector<ResNode> deficit_nodes;

#else //WITHOUT_CAPACITY_SCALING
    typedef Dijkstra<ResGraph, ReducedCostMap, ResDijkstraTraits>
      ResDijkstra;
    /// \brief \ref lemon::Dijkstra "Dijkstra" class for finding
    /// shortest paths in the residual graph with respect to the
    /// reduced edge costs.
    ResDijkstra dijkstra;
    /// \brief Map for identifing deficit nodes.
    DeficitBoolMap has_deficit;
#endif

    /// \brief Pred map for the \ref lemon::Dijkstra "Dijkstra" class.
    typename ResDijkstra::PredMap pred;
    /// \brief Dist map for the \ref lemon::Dijkstra "Dijkstra" class to
    /// update node potentials.
    PotentialUpdateMap updater;

  public :

    /// \brief General constructor of the class (with lower bounds).
    ///
    /// General constructor of the class (with lower bounds).
    ///
    /// \param _graph The directed graph the algorithm runs on.
    /// \param _lower The lower bounds of the edges.
    /// \param _capacity The capacities (upper bounds) of the edges.
    /// \param _cost The cost (length) values of the edges.
    /// \param _supply The supply values of the nodes (signed).
    CapacityScaling( const Graph &_graph,
                     const LowerMap &_lower,
                     const CapacityMap &_capacity,
                     const CostMap &_cost,
                     const SupplyMap &_supply ) :
      graph(_graph), lower(&_lower), capacity(_graph), cost(_cost),
      supply(_graph), flow(_graph, 0), potential(_graph, 0),
      res_graph(_graph, capacity, flow),
      red_cost(res_graph, cost, potential), imbalance(_graph),
#ifdef WITH_SCALING
      delta(0), delta_filter(res_graph, delta),
      dres_graph(res_graph, delta_filter),
      dijkstra(dres_graph, red_cost), pred(dres_graph),
      delta_deficit(imbalance, delta)
#else //WITHOUT_CAPACITY_SCALING
      dijkstra(res_graph, red_cost), pred(res_graph),
      has_deficit(imbalance)
#endif
    {
      // Removing nonzero lower bounds
      capacity = subMap(_capacity, _lower);
      Supply sum = 0;
      for (NodeIt n(graph); n != INVALID; ++n) {
        Supply s = _supply[n];
        for (InEdgeIt e(graph, n); e != INVALID; ++e)
          s += _lower[e];
        for (OutEdgeIt e(graph, n); e != INVALID; ++e)
          s -= _lower[e];
        supply[n] = s;
        sum += s;
      }
      valid_supply = sum == 0;
    }

    /// \brief General constructor of the class (without lower bounds).
    ///
    /// General constructor of the class (without lower bounds).
    ///
    /// \param _graph The directed graph the algorithm runs on.
    /// \param _capacity The capacities (upper bounds) of the edges.
    /// \param _cost The cost (length) values of the edges.
    /// \param _supply The supply values of the nodes (signed).
    CapacityScaling( const Graph &_graph,
                     const CapacityMap &_capacity,
                     const CostMap &_cost,
                     const SupplyMap &_supply ) :
      graph(_graph), lower(NULL), capacity(_capacity), cost(_cost),
      supply(_supply), flow(_graph, 0), potential(_graph, 0),
      res_graph(_graph, capacity, flow),
      red_cost(res_graph, cost, potential), imbalance(_graph),
#ifdef WITH_SCALING
      delta(0), delta_filter(res_graph, delta),
      dres_graph(res_graph, delta_filter),
      dijkstra(dres_graph, red_cost), pred(dres_graph),
      delta_deficit(imbalance, delta)
#else //WITHOUT_CAPACITY_SCALING
      dijkstra(res_graph, red_cost), pred(res_graph),
      has_deficit(imbalance)
#endif
    {
      // Checking 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 of the class (with lower bounds).
    ///
    /// Simple constructor of the class (with lower bounds).
    ///
    /// \param _graph The directed graph the algorithm runs on.
    /// \param _lower The lower bounds of the edges.
    /// \param _capacity The capacities (upper bounds) of the edges.
    /// \param _cost The cost (length) values of the edges.
    /// \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).
    CapacityScaling( const Graph &_graph,
                     const LowerMap &_lower,
                     const CapacityMap &_capacity,
                     const CostMap &_cost,
                     Node _s, Node _t,
                     Supply _flow_value ) :
      graph(_graph), lower(&_lower), capacity(_graph), cost(_cost),
      supply(_graph), flow(_graph, 0), potential(_graph, 0),
      res_graph(_graph, capacity, flow),
      red_cost(res_graph, cost, potential), imbalance(_graph),
#ifdef WITH_SCALING
      delta(0), delta_filter(res_graph, delta),
      dres_graph(res_graph, delta_filter),
      dijkstra(dres_graph, red_cost), pred(dres_graph),
      delta_deficit(imbalance, delta)
#else //WITHOUT_CAPACITY_SCALING
      dijkstra(res_graph, red_cost), pred(res_graph),
      has_deficit(imbalance)
#endif
    {
      // Removing nonzero lower bounds
      capacity = subMap(_capacity, _lower);
      for (NodeIt n(graph); n != INVALID; ++n) {
        Supply s = 0;
        if (n == _s) s =  _flow_value;
        if (n == _t) s = -_flow_value;
        for (InEdgeIt e(graph, n); e != INVALID; ++e)
          s += _lower[e];
        for (OutEdgeIt e(graph, n); e != INVALID; ++e)
          s -= _lower[e];
        supply[n] = s;
      }
      valid_supply = true;
    }

    /// \brief Simple constructor of the class (without lower bounds).
    ///
    /// Simple constructor of the class (without lower bounds).
    ///
    /// \param _graph The directed graph the algorithm runs on.
    /// \param _capacity The capacities (upper bounds) of the edges.
    /// \param _cost The cost (length) values of the edges.
    /// \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).
    CapacityScaling( const Graph &_graph,
                     const CapacityMap &_capacity,
                     const CostMap &_cost,
                     Node _s, Node _t,
                     Supply _flow_value ) :
      graph(_graph), lower(NULL), capacity(_capacity), cost(_cost),
      supply(_graph, 0), flow(_graph, 0), potential(_graph, 0),
      res_graph(_graph, capacity, flow),
      red_cost(res_graph, cost, potential), imbalance(_graph),
#ifdef WITH_SCALING
      delta(0), delta_filter(res_graph, delta),
      dres_graph(res_graph, delta_filter),
      dijkstra(dres_graph, red_cost), pred(dres_graph),
      delta_deficit(imbalance, delta)
#else //WITHOUT_CAPACITY_SCALING
      dijkstra(res_graph, red_cost), pred(res_graph),
      has_deficit(imbalance)
#endif
    {
      supply[_s] =  _flow_value;
      supply[_t] = -_flow_value;
      valid_supply = true;
    }

    /// \brief Returns a const reference to the flow map.
    ///
    /// Returns a const reference to the flow map.
    ///
    /// \pre \ref run() must be called before using this function.
    const FlowMap& flowMap() const {
      return flow;
    }

    /// \brief Returns a const reference to the potential map (the dual
    /// solution).
    ///
    /// Returns a const reference to the potential map (the dual
    /// solution).
    ///
    /// \pre \ref run() must be called before using this function.
    const PotentialMap& potentialMap() const {
      return potential;
    }

    /// \brief Returns the total cost of the found flow.
    ///
    /// Returns 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 (EdgeIt e(graph); e != INVALID; ++e)
        c += flow[e] * cost[e];
      return c;
    }

    /// \brief Runs the algorithm.
    ///
    /// Runs the algorithm.
    ///
    /// \return \c true if a feasible flow can be found.
    bool run() {
      return init() && start();
    }

  protected:

    /// \brief Initializes the algorithm.
    bool init() {
      if (!valid_supply) return false;
      imbalance = supply;

      // Initalizing Dijkstra class
      updater.potentialMap(potential);
      dijkstra.distMap(updater).predMap(pred);

#ifdef WITH_SCALING
      // Initilaizing delta value
      Supply max_sup = 0, max_dem = 0;
      for (NodeIt n(graph); n != INVALID; ++n) {
        if (supply[n] >  max_sup) max_sup =  supply[n];
        if (supply[n] < -max_dem) max_dem = -supply[n];
      }
      if (max_dem < max_sup) max_sup = max_dem;
      for ( delta = 1; SCALING_FACTOR * delta < max_sup;
            delta *= SCALING_FACTOR ) ;
#endif
      return true;
    }

#ifdef WITH_SCALING
    /// \brief Executes the capacity scaling version of the successive
    /// shortest path algorithm.
    bool start() {
      typedef typename DeltaResGraph::EdgeIt DeltaResEdgeIt;
      typedef typename DeltaResGraph::Edge DeltaResEdge;
#ifdef _DEBUG_ITER_
      int dijk_num = 0;
#endif

      // Processing capacity scaling phases
      ResNode s, t;
      for ( ; delta >= 1; delta = delta < SCALING_FACTOR && delta > 1 ?
                                  1 : delta / SCALING_FACTOR )
      {
        // Saturating edges not satisfying the optimality condition
        Capacity r;
        for (DeltaResEdgeIt e(dres_graph); e != INVALID; ++e) {
          if (red_cost[e] < 0) {
            res_graph.augment(e, r = res_graph.rescap(e));
            imbalance[dres_graph.target(e)] += r;
            imbalance[dres_graph.source(e)] -= r;
          }
        }

        // Finding excess nodes
        excess_nodes.clear();
        deficit_nodes.clear();
        for (ResNodeIt n(res_graph); n != INVALID; ++n) {
          if (imbalance[n] >=  delta) excess_nodes.push_back(n);
          if (imbalance[n] <= -delta) deficit_nodes.push_back(n);
        }
        next_node = 0;

        // Finding shortest paths
        while (next_node < excess_nodes.size()) {
          // Checking deficit nodes
          if (delta > 1) {
            bool delta_def = false;
            for (int i = 0; i < deficit_nodes.size(); ++i) {
              if (imbalance[deficit_nodes[i]] <= -delta) {
                delta_def = true;
                break;
              }
            }
            if (!delta_def) break;
          }

          // Running Dijkstra
          s = excess_nodes[next_node];
          updater.init();
          dijkstra.init();
          dijkstra.addSource(s);
#ifdef _DEBUG_ITER_
          ++dijk_num;
#endif
          if ((t = dijkstra.start(delta_deficit)) == INVALID) {
            if (delta > 1) {
              ++next_node;
              continue;
            }
            return false;
          }

          // Updating node potentials
          updater.update();

          // Augment along a shortest path from s to t
          Capacity d = imbalance[s] < -imbalance[t] ?
            imbalance[s] : -imbalance[t];
          ResNode u = t;
          ResEdge e;
          if (d > delta) {
            while ((e = pred[u]) != INVALID) {
              if (res_graph.rescap(e) < d) d = res_graph.rescap(e);
              u = dres_graph.source(e);
            }
          }
          u = t;
          while ((e = pred[u]) != INVALID) {
            res_graph.augment(e, d);
            u = dres_graph.source(e);
          }
          imbalance[s] -= d;
          imbalance[t] += d;
          if (imbalance[s] < delta) ++next_node;
        }
      }
#ifdef _DEBUG_ITER_
      std::cout << "Cost Scaling algorithm finished with running Dijkstra algorithm "
        << dijk_num << " times." << std::endl;
#endif

      // Handling nonzero lower bounds
      if (lower) {
        for (EdgeIt e(graph); e != INVALID; ++e)
          flow[e] += (*lower)[e];
      }
      return true;
    }

#else //WITHOUT_CAPACITY_SCALING
    /// \brief Executes the successive shortest path algorithm without
    /// capacity scaling.
    bool start() {
      // Finding excess nodes
      for (ResNodeIt n(res_graph); n != INVALID; ++n) {
        if (imbalance[n] > 0) excess_nodes.push_back(n);
      }
      if (excess_nodes.size() == 0) return true;
      next_node = 0;

      // Finding shortest paths
      ResNode s, t;
      while ( imbalance[excess_nodes[next_node]] > 0 ||
              ++next_node < excess_nodes.size() )
      {
        // Running Dijkstra
        s = excess_nodes[next_node];
        updater.init();
        dijkstra.init();
        dijkstra.addSource(s);
        if ((t = dijkstra.start(has_deficit)) == INVALID)
          return false;

        // Updating node potentials
        updater.update();

        // Augmenting along a shortest path from s to t
        Capacity delta = imbalance[s] < -imbalance[t] ?
          imbalance[s] : -imbalance[t];
        ResNode u = t;
        ResEdge e;
        while ((e = pred[u]) != INVALID) {
          if (res_graph.rescap(e) < delta) delta = res_graph.rescap(e);
          u = res_graph.source(e);
        }
        u = t;
        while ((e = pred[u]) != INVALID) {
          res_graph.augment(e, delta);
          u = res_graph.source(e);
        }
        imbalance[s] -= delta;
        imbalance[t] += delta;
      }

      // Handling nonzero lower bounds
      if (lower) {
        for (EdgeIt e(graph); e != INVALID; ++e)
          flow[e] += (*lower)[e];
      }
      return true;
    }
#endif

  }; //class CapacityScaling

  ///@}

} //namespace lemon

#endif //LEMON_CAPACITY_SCALING_H