RhodeCode

/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

 * 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_PREFLOW_H

#define LEMON_PREFLOW_H

#include <lemon/tolerance.h>

#include <lemon/elevator.h>

/// \file

/// \ingroup max_flow

/// \brief Implementation of the preflow algorithm.

namespace lemon {

  /// \brief Default traits class of Preflow class.

  ///

  /// Default traits class of Preflow class.

  /// \param _Graph Digraph type.

  /// \param _CapacityMap Type of capacity map.

  template <typename _Graph, typename _CapacityMap>

  struct PreflowDefaultTraits {

    /// \brief The digraph type the algorithm runs on.

    typedef _Graph Digraph;

    /// \brief The type of the map that stores the arc capacities.

    ///

    /// The type of the map that stores the arc capacities.

    /// It must meet the \ref concepts::ReadMap "ReadMap" concept.

    typedef _CapacityMap CapacityMap;

    /// \brief The type of the length of the arcs.

    typedef typename CapacityMap::Value Value;

    /// \brief The map type that stores the flow values.

    ///

    /// The map type that stores the flow values.

    /// It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.

    typedef typename Digraph::template ArcMap<Value> FlowMap;

    /// \brief Instantiates a FlowMap.

    ///

    /// This function instantiates a \ref FlowMap.

    /// \param digraph The digraph, to which we would like to define

    /// the flow map.

    static FlowMap* createFlowMap(const Digraph& digraph) {

      return new FlowMap(digraph);

    }

    /// \brief The eleavator type used by Preflow algorithm.

    ///

    /// The elevator type used by Preflow algorithm.

    ///

    /// \sa Elevator

    /// \sa LinkedElevator

    typedef LinkedElevator<Digraph, typename Digraph::Node> Elevator;

    /// \brief Instantiates an Elevator.

    ///

    /// This function instantiates a \ref Elevator.

    /// \param digraph The digraph, to which we would like to define

    /// the elevator.

    /// \param max_level The maximum level of the elevator.

    static Elevator* createElevator(const Digraph& digraph, int max_level) {

      return new Elevator(digraph, max_level);

    }

    /// \brief The tolerance used by the algorithm

    ///

    /// The tolerance used by the algorithm to handle inexact computation.

    typedef lemon::Tolerance<Value> Tolerance;

  };

  /// \ingroup max_flow

  ///

  /// \brief %Preflow algorithms class.

  ///

  /// This class provides an implementation of the Goldberg's \e

  /// preflow \e algorithm producing a flow of maximum value in a

  /// digraph. The preflow algorithms are the fastest known max

  /// flow algorithms. The current implementation use a mixture of the

  /// \e "highest label" and the \e "bound decrease" heuristics.

  /// The worst case time complexity of the algorithm is \f$O(n^2\sqrt{e})\f$.

  ///

  /// The algorithm consists from two phases. After the first phase

  /// the maximal flow value and the minimum cut can be obtained. The

  /// second phase constructs the feasible maximum flow on each arc.

  ///

  /// \param _Graph The digraph type the algorithm runs on.

  /// \param _CapacityMap The flow map type.

  /// \param _Traits Traits class to set various data types used by

  /// the algorithm.  The default traits class is \ref

  /// PreflowDefaultTraits.  See \ref PreflowDefaultTraits for the

  /// documentation of a %Preflow traits class.

  ///

  ///\author Jacint Szabo and Balazs Dezso

#ifdef DOXYGEN

  template <typename _Graph, typename _CapacityMap, typename _Traits>

#else

  template <typename _Graph,

            typename _CapacityMap = typename _Graph::template ArcMap<int>,

            typename _Traits = PreflowDefaultTraits<_Graph, _CapacityMap> >

#endif

  class Preflow {

  public:

    typedef _Traits Traits;

    typedef typename Traits::Digraph Digraph;

    typedef typename Traits::CapacityMap CapacityMap;

    typedef typename Traits::Value Value;

    typedef typename Traits::FlowMap FlowMap;

    typedef typename Traits::Elevator Elevator;

    typedef typename Traits::Tolerance Tolerance;

  private:

    TEMPLATE_DIGRAPH_TYPEDEFS(Digraph);

    const Digraph& _graph;

    const CapacityMap* _capacity;

    int _node_num;

    Node _source, _target;

    FlowMap* _flow;

    bool _local_flow;

    Elevator* _level;

    bool _local_level;

    typedef typename Digraph::template NodeMap<Value> ExcessMap;

    ExcessMap* _excess;

    Tolerance _tolerance;

    bool _phase;

    void createStructures() {

      _node_num = countNodes(_graph);

      if (!_flow) {

        _flow = Traits::createFlowMap(_graph);

        _local_flow = true;

      }

      if (!_level) {

        _level = Traits::createElevator(_graph, _node_num);

        _local_level = true;

      }

      if (!_excess) {

        _excess = new ExcessMap(_graph);

      }

    }

    void destroyStructures() {

      if (_local_flow) {

        delete _flow;

      }

      if (_local_level) {

        delete _level;

      }

      if (_excess) {

        delete _excess;

      }

    }

  public:

    typedef Preflow Create;

    ///\name Named template parameters

    ///@{

    template <typename _FlowMap>

    struct DefFlowMapTraits : public Traits {

      typedef _FlowMap FlowMap;

      static FlowMap *createFlowMap(const Digraph&) {

      }

    };

    /// \brief \ref named-templ-param "Named parameter" for setting

    /// FlowMap type

    ///

    /// \ref named-templ-param "Named parameter" for setting FlowMap

    /// type

    template <typename _FlowMap>

    struct DefFlowMap

      : public Preflow<Digraph, CapacityMap, DefFlowMapTraits<_FlowMap> > {

      typedef Preflow<Digraph, CapacityMap,

                      DefFlowMapTraits<_FlowMap> > Create;

    };

    template <typename _Elevator>

    struct DefElevatorTraits : public Traits {

      typedef _Elevator Elevator;

      static Elevator *createElevator(const Digraph&, int) {

      }

    };

    /// \brief \ref named-templ-param "Named parameter" for setting

    /// Elevator type

    ///

    /// \ref named-templ-param "Named parameter" for setting Elevator

    /// type

    template <typename _Elevator>

    struct DefElevator

      : public Preflow<Digraph, CapacityMap, DefElevatorTraits<_Elevator> > {

      typedef Preflow<Digraph, CapacityMap,

                      DefElevatorTraits<_Elevator> > Create;

    };

    template <typename _Elevator>

    struct DefStandardElevatorTraits : public Traits {

      typedef _Elevator Elevator;

      static Elevator *createElevator(const Digraph& digraph, int max_level) {

        return new Elevator(digraph, max_level);

      }

    };

    /// \brief \ref named-templ-param "Named parameter" for setting

    /// Elevator type

    ///

    /// \ref named-templ-param "Named parameter" for setting Elevator

    /// type. The Elevator should be standard constructor interface, ie.

    /// the digraph and the maximum level should be passed to it.

    template <typename _Elevator>

    struct DefStandardElevator

      : public Preflow<Digraph, CapacityMap,

                       DefStandardElevatorTraits<_Elevator> > {

      typedef Preflow<Digraph, CapacityMap,

                      DefStandardElevatorTraits<_Elevator> > Create;

    };

    /// @}

  protected:

    Preflow() {}

  public:

    /// \brief The constructor of the class.

    ///

    /// The constructor of the class.

    /// \param digraph The digraph the algorithm runs on.

    /// \param capacity The capacity of the arcs.

    /// \param source The source node.

    /// \param target The target node.

    Preflow(const Digraph& digraph, const CapacityMap& capacity,

               Node source, Node target)

      : _graph(digraph), _capacity(&capacity),

        _node_num(0), _source(source), _target(target),

        _flow(0), _local_flow(false),

        _level(0), _local_level(false),

        _excess(0), _tolerance(), _phase() {}

    /// \brief Destrcutor.

    ///

    /// Destructor.

    ~Preflow() {

      destroyStructures();

    }

    /// \brief Sets the capacity map.

    ///

    /// Sets the capacity map.

    /// \return \c (*this)

    Preflow& capacityMap(const CapacityMap& map) {

      _capacity = ↦

      return *this;

    }

    /// \brief Sets the flow map.

    ///

    /// Sets the flow map.

    /// \return \c (*this)

    Preflow& flowMap(FlowMap& map) {

      if (_local_flow) {

        delete _flow;

        _local_flow = false;

      }

      _flow = ↦

      return *this;

    }

    /// \brief Returns the flow map.

    ///

    /// \return The flow map.

    const FlowMap& flowMap() {

      return *_flow;

    }

    /// \brief Sets the elevator.

    ///

    /// Sets the elevator.

    /// \return \c (*this)

    Preflow& elevator(Elevator& elevator) {

      if (_local_level) {

        delete _level;

        _local_level = false;

      }

      _level = &elevator;

      return *this;

    }

    /// \brief Returns the elevator.

    ///

    /// \return The elevator.

    const Elevator& elevator() {

      return *_level;

    }

    /// \brief Sets the source node.

    ///

    /// Sets the source node.

    /// \return \c (*this)

    Preflow& source(const Node& node) {

      _source = node;

      return *this;

    }

    /// \brief Sets the target node.

    ///

    /// Sets the target node.

    /// \return \c (*this)

    Preflow& target(const Node& node) {

      _target = node;

      return *this;

    }

    /// \brief Sets the tolerance used by algorithm.

    ///

    /// Sets the tolerance used by algorithm.

    Preflow& tolerance(const Tolerance& tolerance) const {

      _tolerance = tolerance;

      return *this;

    }

    /// \brief Returns the tolerance used by algorithm.

    ///

    /// Returns the tolerance used by algorithm.

    const Tolerance& tolerance() const {

      return tolerance;

    }

    /// \name Execution control The simplest way to execute the

    /// algorithm is to use one of the member functions called \c

    /// run().

    /// \n

    /// If you need more control on initial solution or

    /// execution then you have to call one \ref init() function and then

    /// the startFirstPhase() and if you need the startSecondPhase().

    ///@{

    /// \brief Initializes the internal data structures.

    ///

    /// Initializes the internal data structures.

    ///

    void init() {

      createStructures();

      _phase = true;

      for (NodeIt n(_graph); n != INVALID; ++n) {

        _excess->set(n, 0);

      }

      for (ArcIt e(_graph); e != INVALID; ++e) {

        _flow->set(e, 0);

      }

      typename Digraph::template NodeMap<bool> reached(_graph, false);

      _level->initStart();

      _level->initAddItem(_target);

      std::vector<Node> queue;

      reached.set(_source, true);

      queue.push_back(_target);

      reached.set(_target, true);

      while (!queue.empty()) {

        _level->initNewLevel();

        std::vector<Node> nqueue;

        for (int i = 0; i < int(queue.size()); ++i) {

          Node n = queue[i];

          for (InArcIt e(_graph, n); e != INVALID; ++e) {

            Node u = _graph.source(e);

            if (!reached[u] && _tolerance.positive((*_capacity)[e])) {

              reached.set(u, true);

              _level->initAddItem(u);

              nqueue.push_back(u);

            }

          }

        }

        queue.swap(nqueue);

      }

      _level->initFinish();

      for (OutArcIt e(_graph, _source); e != INVALID; ++e) {

        if (_tolerance.positive((*_capacity)[e])) {

          Node u = _graph.target(e);

          if ((*_level)[u] == _level->maxLevel()) continue;

          _flow->set(e, (*_capacity)[e]);

          _excess->set(u, (*_excess)[u] + (*_capacity)[e]);

          if (u != _target && !_level->active(u)) {

            _level->activate(u);

          }

        }

      }

    }

    /// \brief Initializes the internal data structures.

    ///

    /// Initializes the internal data structures and sets the initial

    /// flow to the given \c flowMap. The \c flowMap should contain a

    /// flow or at least a preflow, ie. in each node excluding the

    /// target the incoming flow should greater or equal to the

    /// outgoing flow.

    /// \return %False when the given \c flowMap is not a preflow.

    template <typename FlowMap>

    bool flowInit(const FlowMap& flowMap) {

      createStructures();

      for (ArcIt e(_graph); e != INVALID; ++e) {

        _flow->set(e, flowMap[e]);

      }

      for (NodeIt n(_graph); n != INVALID; ++n) {

        Value excess = 0;

        for (InArcIt e(_graph, n); e != INVALID; ++e) {

          excess += (*_flow)[e];

        }

        for (OutArcIt e(_graph, n); e != INVALID; ++e) {

          excess -= (*_flow)[e];

        }

        if (excess < 0 && n != _source) return false;

        _excess->set(n, excess);

      }

      typename Digraph::template NodeMap<bool> reached(_graph, false);

      _level->initStart();

      _level->initAddItem(_target);

      std::vector<Node> queue;

      reached.set(_source, true);

      queue.push_back(_target);

      reached.set(_target, true);

      while (!queue.empty()) {

        _level->initNewLevel();

        std::vector<Node> nqueue;

        for (int i = 0; i < int(queue.size()); ++i) {

          Node n = queue[i];

          for (InArcIt e(_graph, n); e != INVALID; ++e) {

            Node u = _graph.source(e);

            if (!reached[u] &&

                _tolerance.positive((*_capacity)[e] - (*_flow)[e])) {

              reached.set(u, true);

              _level->initAddItem(u);

              nqueue.push_back(u);

            }

          }

          for (OutArcIt e(_graph, n); e != INVALID; ++e) {

            Node v = _graph.target(e);

            if (!reached[v] && _tolerance.positive((*_flow)[e])) {

              reached.set(v, true);

              _level->initAddItem(v);

              nqueue.push_back(v);

            }

          }

        }

        queue.swap(nqueue);

      }

      _level->initFinish();

      for (OutArcIt e(_graph, _source); e != INVALID; ++e) {

        Value rem = (*_capacity)[e] - (*_flow)[e];

        if (_tolerance.positive(rem)) {

          Node u = _graph.target(e);

          if ((*_level)[u] == _level->maxLevel()) continue;

          _flow->set(e, (*_capacity)[e]);

          _excess->set(u, (*_excess)[u] + rem);

          if (u != _target && !_level->active(u)) {

            _level->activate(u);

          }

        }

      }

      for (InArcIt e(_graph, _source); e != INVALID; ++e) {

        Value rem = (*_flow)[e];

        if (_tolerance.positive(rem)) {

          Node v = _graph.source(e);

          if ((*_level)[v] == _level->maxLevel()) continue;

          _flow->set(e, 0);

          _excess->set(v, (*_excess)[v] + rem);

          if (v != _target && !_level->active(v)) {

            _level->activate(v);

          }

        }

      }

      return true;

    }

    /// \brief Starts the first phase of the preflow algorithm.

    ///

    /// The preflow algorithm consists of two phases, this method runs

    /// the first phase. After the first phase the maximum flow value

    /// and a minimum value cut can already be computed, although a

    /// maximum flow is not yet obtained. So after calling this method

    /// \ref flowValue() returns the value of a maximum flow and \ref

    /// minCut() returns a minimum cut.

    /// \pre One of the \ref init() functions should be called.

    void startFirstPhase() {

      _phase = true;

      Node n = _level->highestActive();

      int level = _level->highestActiveLevel();

      while (n != INVALID) {

        int num = _node_num;

        while (num > 0 && n != INVALID) {

          Value excess = (*_excess)[n];

          int new_level = _level->maxLevel();

          for (OutArcIt e(_graph, n); e != INVALID; ++e) {

            Value rem = (*_capacity)[e] - (*_flow)[e];

            if (!_tolerance.positive(rem)) continue;

            Node v = _graph.target(e);

            if ((*_level)[v] < level) {

              if (!_level->active(v) && v != _target) {

                _level->activate(v);

              }

              if (!_tolerance.less(rem, excess)) {

                _flow->set(e, (*_flow)[e] + excess);

                _excess->set(v, (*_excess)[v] + excess);

                excess = 0;

                goto no_more_push_1;

              } else {

                excess -= rem;

                _excess->set(v, (*_excess)[v] + rem);

                _flow->set(e, (*_capacity)[e]);

              }

            } else if (new_level > (*_level)[v]) {

              new_level = (*_level)[v];

            }

          }

          for (InArcIt e(_graph, n); e != INVALID; ++e) {

            Value rem = (*_flow)[e];

            if (!_tolerance.positive(rem)) continue;

            Node v = _graph.source(e);

            if ((*_level)[v] < level) {

              if (!_level->active(v) && v != _target) {

                _level->activate(v);

              }

              if (!_tolerance.less(rem, excess)) {

                _flow->set(e, (*_flow)[e] - excess);

                _excess->set(v, (*_excess)[v] + excess);

                excess = 0;

                goto no_more_push_1;

              } else {

                excess -= rem;

                _excess->set(v, (*_excess)[v] + rem);

                _flow->set(e, 0);

              }

            } else if (new_level > (*_level)[v]) {

              new_level = (*_level)[v];

            }

          }

        no_more_push_1:

          _excess->set(n, excess);

          if (excess != 0) {

            if (new_level + 1 < _level->maxLevel()) {

              _level->liftHighestActive(new_level + 1);

            } else {

              _level->liftHighestActiveToTop();

            }

            if (_level->emptyLevel(level)) {

              _level->liftToTop(level);

            }

          } else {

            _level->deactivate(n);

          }

          n = _level->highestActive();

          level = _level->highestActiveLevel();

          --num;

        }

        num = _node_num * 20;

        while (num > 0 && n != INVALID) {

          Value excess = (*_excess)[n];

          int new_level = _level->maxLevel();

          for (OutArcIt e(_graph, n); e != INVALID; ++e) {

            Value rem = (*_capacity)[e] - (*_flow)[e];

            if (!_tolerance.positive(rem)) continue;

            Node v = _graph.target(e);

            if ((*_level)[v] < level) {

              if (!_level->active(v) && v != _target) {

                _level->activate(v);

              }

              if (!_tolerance.less(rem, excess)) {

                _flow->set(e, (*_flow)[e] + excess);

                _excess->set(v, (*_excess)[v] + excess);

                excess = 0;

                goto no_more_push_2;

              } else {

                excess -= rem;

                _excess->set(v, (*_excess)[v] + rem);

                _flow->set(e, (*_capacity)[e]);

              }

            } else if (new_level > (*_level)[v]) {

              new_level = (*_level)[v];

            }

          }

          for (InArcIt e(_graph, n); e != INVALID; ++e) {

            Value rem = (*_flow)[e];

            if (!_tolerance.positive(rem)) continue;

            Node v = _graph.source(e);

            if ((*_level)[v] < level) {

              if (!_level->active(v) && v != _target) {

                _level->activate(v);

              }

              if (!_tolerance.less(rem, excess)) {

                _flow->set(e, (*_flow)[e] - excess);

                _excess->set(v, (*_excess)[v] + excess);

                excess = 0;

                goto no_more_push_2;

              } else {

                excess -= rem;

                _excess->set(v, (*_excess)[v] + rem);

                _flow->set(e, 0);

              }

            } else if (new_level > (*_level)[v]) {

              new_level = (*_level)[v];

            }

          }

        no_more_push_2:

          _excess->set(n, excess);

          if (excess != 0) {

            if (new_level + 1 < _level->maxLevel()) {

              _level->liftActiveOn(level, new_level + 1);

            } else {

              _level->liftActiveToTop(level);

            }

            if (_level->emptyLevel(level)) {

              _level->liftToTop(level);

            }

          } else {

            _level->deactivate(n);

          }

          while (level >= 0 && _level->activeFree(level)) {

            --level;

          }

          if (level == -1) {

            n = _level->highestActive();

            level = _level->highestActiveLevel();

          } else {

            n = _level->activeOn(level);

          }

          --num;

        }

      }

    }

    /// \brief Starts the second phase of the preflow algorithm.

    ///

    /// The preflow algorithm consists of two phases, this method runs

    /// the second phase. After calling \ref init() and \ref

    /// startFirstPhase() and then \ref startSecondPhase(), \ref

    /// flowMap() return a maximum flow, \ref flowValue() returns the

    /// value of a maximum flow, \ref minCut() returns a minimum cut

    /// \pre The \ref init() and startFirstPhase() functions should be

    /// called before.

    void startSecondPhase() {

      _phase = false;

      typename Digraph::template NodeMap<bool> reached(_graph);

      for (NodeIt n(_graph); n != INVALID; ++n) {

        reached.set(n, (*_level)[n] < _level->maxLevel());

      }

      _level->initStart();

      _level->initAddItem(_source);

      std::vector<Node> queue;

      queue.push_back(_source);

      reached.set(_source, true);

      while (!queue.empty()) {

        _level->initNewLevel();

        std::vector<Node> nqueue;

        for (int i = 0; i < int(queue.size()); ++i) {

          Node n = queue[i];

          for (OutArcIt e(_graph, n); e != INVALID; ++e) {

            Node v = _graph.target(e);

            if (!reached[v] && _tolerance.positive((*_flow)[e])) {

              reached.set(v, true);

              _level->initAddItem(v);

              nqueue.push_back(v);

            }

          }

          for (InArcIt e(_graph, n); e != INVALID; ++e) {

            Node u = _graph.source(e);

            if (!reached[u] &&

                _tolerance.positive((*_capacity)[e] - (*_flow)[e])) {

              reached.set(u, true);

              _level->initAddItem(u);

              nqueue.push_back(u);

            }

          }

        }

        queue.swap(nqueue);

      }

      _level->initFinish();

      for (NodeIt n(_graph); n != INVALID; ++n) {

        if (!reached[n]) {

          _level->dirtyTopButOne(n);

        } else if ((*_excess)[n] > 0 && _target != n) {

          _level->activate(n);

        }

      }

      Node n;

      while ((n = _level->highestActive()) != INVALID) {

        Value excess = (*_excess)[n];

        int level = _level->highestActiveLevel();

        int new_level = _level->maxLevel();

        for (OutArcIt e(_graph, n); e != INVALID; ++e) {

          Value rem = (*_capacity)[e] - (*_flow)[e];

          if (!_tolerance.positive(rem)) continue;

          Node v = _graph.target(e);

          if ((*_level)[v] < level) {

            if (!_level->active(v) && v != _source) {

              _level->activate(v);

            }

            if (!_tolerance.less(rem, excess)) {

              _flow->set(e, (*_flow)[e] + excess);

              _excess->set(v, (*_excess)[v] + excess);

              excess = 0;

              goto no_more_push;

            } else {

              excess -= rem;

              _excess->set(v, (*_excess)[v] + rem);

              _flow->set(e, (*_capacity)[e]);

            }

          } else if (new_level > (*_level)[v]) {

            new_level = (*_level)[v];

          }

        }

        for (InArcIt e(_graph, n); e != INVALID; ++e) {

          Value rem = (*_flow)[e];

          if (!_tolerance.positive(rem)) continue;

          Node v = _graph.source(e);

          if ((*_level)[v] < level) {

            if (!_level->active(v) && v != _source) {

              _level->activate(v);

            }

            if (!_tolerance.less(rem, excess)) {

              _flow->set(e, (*_flow)[e] - excess);

              _excess->set(v, (*_excess)[v] + excess);

              excess = 0;

              goto no_more_push;

            } else {

              excess -= rem;

              _excess->set(v, (*_excess)[v] + rem);

              _flow->set(e, 0);

            }

          } else if (new_level > (*_level)[v]) {

            new_level = (*_level)[v];

          }

        }

      no_more_push:

        _excess->set(n, excess);

        if (excess != 0) {

          if (new_level + 1 < _level->maxLevel()) {

            _level->liftHighestActive(new_level + 1);

          } else {

            // Calculation error

            _level->liftHighestActiveToTop();

          }

          if (_level->emptyLevel(level)) {

            // Calculation error

            _level->liftToTop(level);

          }

        } else {

          _level->deactivate(n);

        }

      }

    }

    /// \brief Runs the preflow algorithm.

    ///

    /// Runs the preflow algorithm.

    /// \note pf.run() is just a shortcut of the following code.

    /// \code

    ///   pf.init();

    ///   pf.startFirstPhase();

    ///   pf.startSecondPhase();

    /// \endcode

    void run() {

      init();

      startFirstPhase();

      startSecondPhase();

    }

    /// \brief Runs the preflow algorithm to compute the minimum cut.

    ///

    /// Runs the preflow algorithm to compute the minimum cut.

    /// \note pf.runMinCut() is just a shortcut of the following code.

    /// \code

    ///   pf.init();

    ///   pf.startFirstPhase();

    /// \endcode

    void runMinCut() {

      init();

      startFirstPhase();

    }

    /// @}

    /// \name Query Functions

    /// The result of the %Preflow algorithm can be obtained using these

    /// functions.\n

    /// Before the use of these functions,

    /// either run() or start() must be called.

    ///@{

    /// \brief Returns the value of the maximum flow.

    ///

    /// Returns the value of the maximum flow by returning the excess

    /// of the target node \c t. This value equals to the value of

    /// the maximum flow already after the first phase.

    Value flowValue() const {

      return (*_excess)[_target];

    }

    /// \brief Returns true when the node is on the source side of minimum cut.

    ///

    /// Returns true when the node is on the source side of minimum

    /// cut. This method can be called both after running \ref

    /// startFirstPhase() and \ref startSecondPhase().

    bool minCut(const Node& node) const {

      return ((*_level)[node] == _level->maxLevel()) == _phase;

    }

    /// \brief Returns a minimum value cut.

    ///

    /// Sets the \c cutMap to the characteristic vector of a minimum value

    /// cut. This method can be called both after running \ref

    /// startFirstPhase() and \ref startSecondPhase(). The result after second

    /// phase could be changed slightly if inexact computation is used.

    /// \pre The \c cutMap should be a bool-valued node-map.

    template <typename CutMap>

    void minCutMap(CutMap& cutMap) const {

      for (NodeIt n(_graph); n != INVALID; ++n) {

        cutMap.set(n, minCut(n));

      }

    }

    /// \brief Returns the flow on the arc.

    ///

    /// Sets the \c flowMap to the flow on the arcs. This method can

    /// be called after the second phase of algorithm.

    Value flow(const Arc& arc) const {

      return (*_flow)[arc];

    }

    /// @}

  };

}

#endif