diff -r 98a30824fe36 -r ece80147fb08 lemon/bellman_ford.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lemon/bellman_ford.h	Fri Sep 25 09:06:32 2009 +0200
@@ -0,0 +1,1100 @@
+/* -*- 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_BELLMAN_FORD_H
+#define LEMON_BELLMAN_FORD_H
+
+/// \ingroup shortest_path
+/// \file
+/// \brief Bellman-Ford algorithm.
+
+#include <lemon/bits/path_dump.h>
+#include <lemon/core.h>
+#include <lemon/error.h>
+#include <lemon/maps.h>
+#include <lemon/path.h>
+
+#include <limits>
+
+namespace lemon {
+
+  /// \brief Default OperationTraits for the BellmanFord algorithm class.
+  ///  
+  /// This operation traits class defines all computational operations
+  /// and constants that are used in the Bellman-Ford algorithm.
+  /// The default implementation is based on the \c numeric_limits class.
+  /// If the numeric type does not have infinity value, then the maximum
+  /// value is used as extremal infinity value.
+  template <
+    typename V, 
+    bool has_inf = std::numeric_limits<V>::has_infinity>
+  struct BellmanFordDefaultOperationTraits {
+    /// \e
+    typedef V Value;
+    /// \brief Gives back the zero value of the type.
+    static Value zero() {
+      return static_cast<Value>(0);
+    }
+    /// \brief Gives back the positive infinity value of the type.
+    static Value infinity() {
+      return std::numeric_limits<Value>::infinity();
+    }
+    /// \brief Gives back the sum of the given two elements.
+    static Value plus(const Value& left, const Value& right) {
+      return left + right;
+    }
+    /// \brief Gives back \c true only if the first value is less than
+    /// the second.
+    static bool less(const Value& left, const Value& right) {
+      return left < right;
+    }
+  };
+
+  template <typename V>
+  struct BellmanFordDefaultOperationTraits<V, false> {
+    typedef V Value;
+    static Value zero() {
+      return static_cast<Value>(0);
+    }
+    static Value infinity() {
+      return std::numeric_limits<Value>::max();
+    }
+    static Value plus(const Value& left, const Value& right) {
+      if (left == infinity() || right == infinity()) return infinity();
+      return left + right;
+    }
+    static bool less(const Value& left, const Value& right) {
+      return left < right;
+    }
+  };
+  
+  /// \brief Default traits class of BellmanFord class.
+  ///
+  /// Default traits class of BellmanFord class.
+  /// \param GR The type of the digraph.
+  /// \param LEN The type of the length map.
+  template<typename GR, typename LEN>
+  struct BellmanFordDefaultTraits {
+    /// The type of the digraph the algorithm runs on. 
+    typedef GR Digraph;
+
+    /// \brief The type of the map that stores the arc lengths.
+    ///
+    /// The type of the map that stores the arc lengths.
+    /// It must conform to the \ref concepts::ReadMap "ReadMap" concept.
+    typedef LEN LengthMap;
+
+    /// The type of the arc lengths.
+    typedef typename LEN::Value Value;
+
+    /// \brief Operation traits for Bellman-Ford algorithm.
+    ///
+    /// It defines the used operations and the infinity value for the
+    /// given \c Value type.
+    /// \see BellmanFordDefaultOperationTraits
+    typedef BellmanFordDefaultOperationTraits<Value> OperationTraits;
+ 
+    /// \brief The type of the map that stores the last arcs of the 
+    /// shortest paths.
+    /// 
+    /// The type of the map that stores the last
+    /// arcs of the shortest paths.
+    /// It must conform to the \ref concepts::WriteMap "WriteMap" concept.
+    typedef typename GR::template NodeMap<typename GR::Arc> PredMap;
+
+    /// \brief Instantiates a \c PredMap.
+    /// 
+    /// This function instantiates a \ref PredMap. 
+    /// \param g is the digraph to which we would like to define the
+    /// \ref PredMap.
+    static PredMap *createPredMap(const GR& g) {
+      return new PredMap(g);
+    }
+
+    /// \brief The type of the map that stores the distances of the nodes.
+    ///
+    /// The type of the map that stores the distances of the nodes.
+    /// It must conform to the \ref concepts::WriteMap "WriteMap" concept.
+    typedef typename GR::template NodeMap<typename LEN::Value> DistMap;
+
+    /// \brief Instantiates a \c DistMap.
+    ///
+    /// This function instantiates a \ref DistMap. 
+    /// \param g is the digraph to which we would like to define the 
+    /// \ref DistMap.
+    static DistMap *createDistMap(const GR& g) {
+      return new DistMap(g);
+    }
+
+  };
+  
+  /// \brief %BellmanFord algorithm class.
+  ///
+  /// \ingroup shortest_path
+  /// This class provides an efficient implementation of the Bellman-Ford 
+  /// algorithm. The maximum time complexity of the algorithm is
+  /// <tt>O(ne)</tt>.
+  ///
+  /// The Bellman-Ford algorithm solves the single-source shortest path
+  /// problem when the arcs can have negative lengths, but the digraph
+  /// should not contain directed cycles with negative total length.
+  /// If all arc costs are non-negative, consider to use the Dijkstra
+  /// algorithm instead, since it is more efficient.
+  ///
+  /// The arc lengths are passed to the algorithm using a
+  /// \ref concepts::ReadMap "ReadMap", so it is easy to change it to any 
+  /// kind of length. The type of the length values is determined by the
+  /// \ref concepts::ReadMap::Value "Value" type of the length map.
+  ///
+  /// There is also a \ref bellmanFord() "function-type interface" for the
+  /// Bellman-Ford algorithm, which is convenient in the simplier cases and
+  /// it can be used easier.
+  ///
+  /// \tparam GR The type of the digraph the algorithm runs on.
+  /// The default type is \ref ListDigraph.
+  /// \tparam LEN A \ref concepts::ReadMap "readable" arc map that specifies
+  /// the lengths of the arcs. The default map type is
+  /// \ref concepts::Digraph::ArcMap "GR::ArcMap<int>".
+#ifdef DOXYGEN
+  template <typename GR, typename LEN, typename TR>
+#else
+  template <typename GR=ListDigraph,
+            typename LEN=typename GR::template ArcMap<int>,
+            typename TR=BellmanFordDefaultTraits<GR,LEN> >
+#endif
+  class BellmanFord {
+  public:
+
+    ///The type of the underlying digraph.
+    typedef typename TR::Digraph Digraph;
+    
+    /// \brief The type of the arc lengths.
+    typedef typename TR::LengthMap::Value Value;
+    /// \brief The type of the map that stores the arc lengths.
+    typedef typename TR::LengthMap LengthMap;
+    /// \brief The type of the map that stores the last
+    /// arcs of the shortest paths.
+    typedef typename TR::PredMap PredMap;
+    /// \brief The type of the map that stores the distances of the nodes.
+    typedef typename TR::DistMap DistMap;
+    /// The type of the paths.
+    typedef PredMapPath<Digraph, PredMap> Path;
+    ///\brief The \ref BellmanFordDefaultOperationTraits
+    /// "operation traits class" of the algorithm.
+    typedef typename TR::OperationTraits OperationTraits;
+
+    ///The \ref BellmanFordDefaultTraits "traits class" of the algorithm.
+    typedef TR Traits;
+
+  private:
+
+    typedef typename Digraph::Node Node;
+    typedef typename Digraph::NodeIt NodeIt;
+    typedef typename Digraph::Arc Arc;
+    typedef typename Digraph::OutArcIt OutArcIt;
+
+    // Pointer to the underlying digraph.
+    const Digraph *_gr;
+    // Pointer to the length map
+    const LengthMap *_length;
+    // Pointer to the map of predecessors arcs.
+    PredMap *_pred;
+    // Indicates if _pred is locally allocated (true) or not.
+    bool _local_pred;
+    // Pointer to the map of distances.
+    DistMap *_dist;
+    // Indicates if _dist is locally allocated (true) or not.
+    bool _local_dist;
+
+    typedef typename Digraph::template NodeMap<bool> MaskMap;
+    MaskMap *_mask;
+
+    std::vector<Node> _process;
+
+    // Creates the maps if necessary.
+    void create_maps() {
+      if(!_pred) {
+	_local_pred = true;
+	_pred = Traits::createPredMap(*_gr);
+      }
+      if(!_dist) {
+	_local_dist = true;
+	_dist = Traits::createDistMap(*_gr);
+      }
+      _mask = new MaskMap(*_gr, false);
+    }
+    
+  public :
+ 
+    typedef BellmanFord Create;
+
+    /// \name Named Template Parameters
+
+    ///@{
+
+    template <class T>
+    struct SetPredMapTraits : public Traits {
+      typedef T PredMap;
+      static PredMap *createPredMap(const Digraph&) {
+        LEMON_ASSERT(false, "PredMap is not initialized");
+        return 0; // ignore warnings
+      }
+    };
+
+    /// \brief \ref named-templ-param "Named parameter" for setting
+    /// \c PredMap type.
+    ///
+    /// \ref named-templ-param "Named parameter" for setting
+    /// \c PredMap type.
+    /// It must conform to the \ref concepts::WriteMap "WriteMap" concept.
+    template <class T>
+    struct SetPredMap 
+      : public BellmanFord< Digraph, LengthMap, SetPredMapTraits<T> > {
+      typedef BellmanFord< Digraph, LengthMap, SetPredMapTraits<T> > Create;
+    };
+    
+    template <class T>
+    struct SetDistMapTraits : public Traits {
+      typedef T DistMap;
+      static DistMap *createDistMap(const Digraph&) {
+        LEMON_ASSERT(false, "DistMap is not initialized");
+        return 0; // ignore warnings
+      }
+    };
+
+    /// \brief \ref named-templ-param "Named parameter" for setting
+    /// \c DistMap type.
+    ///
+    /// \ref named-templ-param "Named parameter" for setting
+    /// \c DistMap type.
+    /// It must conform to the \ref concepts::WriteMap "WriteMap" concept.
+    template <class T>
+    struct SetDistMap 
+      : public BellmanFord< Digraph, LengthMap, SetDistMapTraits<T> > {
+      typedef BellmanFord< Digraph, LengthMap, SetDistMapTraits<T> > Create;
+    };
+
+    template <class T>
+    struct SetOperationTraitsTraits : public Traits {
+      typedef T OperationTraits;
+    };
+    
+    /// \brief \ref named-templ-param "Named parameter" for setting 
+    /// \c OperationTraits type.
+    ///
+    /// \ref named-templ-param "Named parameter" for setting
+    /// \c OperationTraits type.
+    /// For more information see \ref BellmanFordDefaultOperationTraits.
+    template <class T>
+    struct SetOperationTraits
+      : public BellmanFord< Digraph, LengthMap, SetOperationTraitsTraits<T> > {
+      typedef BellmanFord< Digraph, LengthMap, SetOperationTraitsTraits<T> >
+      Create;
+    };
+    
+    ///@}
+
+  protected:
+    
+    BellmanFord() {}
+
+  public:      
+    
+    /// \brief Constructor.
+    ///
+    /// Constructor.
+    /// \param g The digraph the algorithm runs on.
+    /// \param length The length map used by the algorithm.
+    BellmanFord(const Digraph& g, const LengthMap& length) :
+      _gr(&g), _length(&length),
+      _pred(0), _local_pred(false),
+      _dist(0), _local_dist(false), _mask(0) {}
+    
+    ///Destructor.
+    ~BellmanFord() {
+      if(_local_pred) delete _pred;
+      if(_local_dist) delete _dist;
+      if(_mask) delete _mask;
+    }
+
+    /// \brief Sets the length map.
+    ///
+    /// Sets the length map.
+    /// \return <tt>(*this)</tt>
+    BellmanFord &lengthMap(const LengthMap &map) {
+      _length = &map;
+      return *this;
+    }
+
+    /// \brief Sets the map that stores the predecessor arcs.
+    ///
+    /// Sets the map that stores the predecessor arcs.
+    /// If you don't use this function before calling \ref run()
+    /// or \ref init(), an instance will be allocated automatically.
+    /// The destructor deallocates this automatically allocated map,
+    /// of course.
+    /// \return <tt>(*this)</tt>
+    BellmanFord &predMap(PredMap &map) {
+      if(_local_pred) {
+	delete _pred;
+	_local_pred=false;
+      }
+      _pred = &map;
+      return *this;
+    }
+
+    /// \brief Sets the map that stores the distances of the nodes.
+    ///
+    /// Sets the map that stores the distances of the nodes calculated
+    /// by the algorithm.
+    /// If you don't use this function before calling \ref run()
+    /// or \ref init(), an instance will be allocated automatically.
+    /// The destructor deallocates this automatically allocated map,
+    /// of course.
+    /// \return <tt>(*this)</tt>
+    BellmanFord &distMap(DistMap &map) {
+      if(_local_dist) {
+	delete _dist;
+	_local_dist=false;
+      }
+      _dist = &map;
+      return *this;
+    }
+
+    /// \name Execution Control
+    /// The simplest way to execute the Bellman-Ford algorithm is to use
+    /// one of the member functions called \ref run().\n
+    /// If you need better control on the execution, you have to call
+    /// \ref init() first, then you can add several source nodes
+    /// with \ref addSource(). Finally the actual path computation can be
+    /// performed with \ref start(), \ref checkedStart() or
+    /// \ref limitedStart().
+
+    ///@{
+
+    /// \brief Initializes the internal data structures.
+    /// 
+    /// Initializes the internal data structures. The optional parameter
+    /// is the initial distance of each node.
+    void init(const Value value = OperationTraits::infinity()) {
+      create_maps();
+      for (NodeIt it(*_gr); it != INVALID; ++it) {
+	_pred->set(it, INVALID);
+	_dist->set(it, value);
+      }
+      _process.clear();
+      if (OperationTraits::less(value, OperationTraits::infinity())) {
+	for (NodeIt it(*_gr); it != INVALID; ++it) {
+	  _process.push_back(it);
+	  _mask->set(it, true);
+	}
+      }
+    }
+    
+    /// \brief Adds a new source node.
+    ///
+    /// This function adds a new source node. The optional second parameter
+    /// is the initial distance of the node.
+    void addSource(Node source, Value dst = OperationTraits::zero()) {
+      _dist->set(source, dst);
+      if (!(*_mask)[source]) {
+	_process.push_back(source);
+	_mask->set(source, true);
+      }
+    }
+
+    /// \brief Executes one round from the Bellman-Ford algorithm.
+    ///
+    /// If the algoritm calculated the distances in the previous round
+    /// exactly for the paths of at most \c k arcs, then this function
+    /// will calculate the distances exactly for the paths of at most
+    /// <tt>k+1</tt> arcs. Performing \c k iterations using this function
+    /// calculates the shortest path distances exactly for the paths
+    /// consisting of at most \c k arcs.
+    ///
+    /// \warning The paths with limited arc number cannot be retrieved
+    /// easily with \ref path() or \ref predArc() functions. If you also
+    /// need the shortest paths and not only the distances, you should
+    /// store the \ref predMap() "predecessor map" after each iteration
+    /// and build the path manually.
+    ///
+    /// \return \c true when the algorithm have not found more shorter
+    /// paths.
+    ///
+    /// \see ActiveIt
+    bool processNextRound() {
+      for (int i = 0; i < int(_process.size()); ++i) {
+	_mask->set(_process[i], false);
+      }
+      std::vector<Node> nextProcess;
+      std::vector<Value> values(_process.size());
+      for (int i = 0; i < int(_process.size()); ++i) {
+	values[i] = (*_dist)[_process[i]];
+      }
+      for (int i = 0; i < int(_process.size()); ++i) {
+	for (OutArcIt it(*_gr, _process[i]); it != INVALID; ++it) {
+	  Node target = _gr->target(it);
+	  Value relaxed = OperationTraits::plus(values[i], (*_length)[it]);
+	  if (OperationTraits::less(relaxed, (*_dist)[target])) {
+	    _pred->set(target, it);
+	    _dist->set(target, relaxed);
+	    if (!(*_mask)[target]) {
+	      _mask->set(target, true);
+	      nextProcess.push_back(target);
+	    }
+	  }	  
+	}
+      }
+      _process.swap(nextProcess);
+      return _process.empty();
+    }
+
+    /// \brief Executes one weak round from the Bellman-Ford algorithm.
+    ///
+    /// If the algorithm calculated the distances in the previous round
+    /// at least for the paths of at most \c k arcs, then this function
+    /// will calculate the distances at least for the paths of at most
+    /// <tt>k+1</tt> arcs.
+    /// This function does not make it possible to calculate the shortest
+    /// path distances exactly for paths consisting of at most \c k arcs,
+    /// this is why it is called weak round.
+    ///
+    /// \return \c true when the algorithm have not found more shorter
+    /// paths.
+    ///
+    /// \see ActiveIt
+    bool processNextWeakRound() {
+      for (int i = 0; i < int(_process.size()); ++i) {
+	_mask->set(_process[i], false);
+      }
+      std::vector<Node> nextProcess;
+      for (int i = 0; i < int(_process.size()); ++i) {
+	for (OutArcIt it(*_gr, _process[i]); it != INVALID; ++it) {
+	  Node target = _gr->target(it);
+	  Value relaxed = 
+	    OperationTraits::plus((*_dist)[_process[i]], (*_length)[it]);
+	  if (OperationTraits::less(relaxed, (*_dist)[target])) {
+	    _pred->set(target, it);
+	    _dist->set(target, relaxed);
+	    if (!(*_mask)[target]) {
+	      _mask->set(target, true);
+	      nextProcess.push_back(target);
+	    }
+	  }	  
+	}
+      }
+      _process.swap(nextProcess);
+      return _process.empty();
+    }
+
+    /// \brief Executes the algorithm.
+    ///
+    /// Executes the algorithm.
+    ///
+    /// This method runs the Bellman-Ford algorithm from the root node(s)
+    /// in order to compute the shortest path to each node.
+    ///
+    /// The algorithm computes
+    /// - the shortest path tree (forest),
+    /// - the distance of each node from the root(s).
+    ///
+    /// \pre init() must be called and at least one root node should be
+    /// added with addSource() before using this function.
+    void start() {
+      int num = countNodes(*_gr) - 1;
+      for (int i = 0; i < num; ++i) {
+	if (processNextWeakRound()) break;
+      }
+    }
+
+    /// \brief Executes the algorithm and checks the negative cycles.
+    ///
+    /// Executes the algorithm and checks the negative cycles.
+    ///
+    /// This method runs the Bellman-Ford algorithm from the root node(s)
+    /// in order to compute the shortest path to each node and also checks
+    /// if the digraph contains cycles with negative total length.
+    ///
+    /// The algorithm computes 
+    /// - the shortest path tree (forest),
+    /// - the distance of each node from the root(s).
+    /// 
+    /// \return \c false if there is a negative cycle in the digraph.
+    ///
+    /// \pre init() must be called and at least one root node should be
+    /// added with addSource() before using this function. 
+    bool checkedStart() {
+      int num = countNodes(*_gr);
+      for (int i = 0; i < num; ++i) {
+	if (processNextWeakRound()) return true;
+      }
+      return _process.empty();
+    }
+
+    /// \brief Executes the algorithm with arc number limit.
+    ///
+    /// Executes the algorithm with arc number limit.
+    ///
+    /// This method runs the Bellman-Ford algorithm from the root node(s)
+    /// in order to compute the shortest path distance for each node
+    /// using only the paths consisting of at most \c num arcs.
+    ///
+    /// The algorithm computes
+    /// - the limited distance of each node from the root(s),
+    /// - the predecessor arc for each node.
+    ///
+    /// \warning The paths with limited arc number cannot be retrieved
+    /// easily with \ref path() or \ref predArc() functions. If you also
+    /// need the shortest paths and not only the distances, you should
+    /// store the \ref predMap() "predecessor map" after each iteration
+    /// and build the path manually.
+    ///
+    /// \pre init() must be called and at least one root node should be
+    /// added with addSource() before using this function. 
+    void limitedStart(int num) {
+      for (int i = 0; i < num; ++i) {
+	if (processNextRound()) break;
+      }
+    }
+    
+    /// \brief Runs the algorithm from the given root node.
+    ///    
+    /// This method runs the Bellman-Ford algorithm from the given root
+    /// node \c s in order to compute the shortest path to each node.
+    ///
+    /// The algorithm computes
+    /// - the shortest path tree (forest),
+    /// - the distance of each node from the root(s).
+    ///
+    /// \note bf.run(s) is just a shortcut of the following code.
+    /// \code
+    ///   bf.init();
+    ///   bf.addSource(s);
+    ///   bf.start();
+    /// \endcode
+    void run(Node s) {
+      init();
+      addSource(s);
+      start();
+    }
+    
+    /// \brief Runs the algorithm from the given root node with arc
+    /// number limit.
+    ///    
+    /// This method runs the Bellman-Ford algorithm from the given root
+    /// node \c s in order to compute the shortest path distance for each
+    /// node using only the paths consisting of at most \c num arcs.
+    ///
+    /// The algorithm computes
+    /// - the limited distance of each node from the root(s),
+    /// - the predecessor arc for each node.
+    ///
+    /// \warning The paths with limited arc number cannot be retrieved
+    /// easily with \ref path() or \ref predArc() functions. If you also
+    /// need the shortest paths and not only the distances, you should
+    /// store the \ref predMap() "predecessor map" after each iteration
+    /// and build the path manually.
+    ///
+    /// \note bf.run(s, num) is just a shortcut of the following code.
+    /// \code
+    ///   bf.init();
+    ///   bf.addSource(s);
+    ///   bf.limitedStart(num);
+    /// \endcode
+    void run(Node s, int num) {
+      init();
+      addSource(s);
+      limitedStart(num);
+    }
+    
+    ///@}
+
+    /// \brief LEMON iterator for getting the active nodes.
+    ///
+    /// This class provides a common style LEMON iterator that traverses
+    /// the active nodes of the Bellman-Ford algorithm after the last
+    /// phase. These nodes should be checked in the next phase to
+    /// find augmenting arcs outgoing from them.
+    class ActiveIt {
+    public:
+
+      /// \brief Constructor.
+      ///
+      /// Constructor for getting the active nodes of the given BellmanFord
+      /// instance. 
+      ActiveIt(const BellmanFord& algorithm) : _algorithm(&algorithm)
+      {
+        _index = _algorithm->_process.size() - 1;
+      }
+
+      /// \brief Invalid constructor.
+      ///
+      /// Invalid constructor.
+      ActiveIt(Invalid) : _algorithm(0), _index(-1) {}
+
+      /// \brief Conversion to \c Node.
+      ///
+      /// Conversion to \c Node.
+      operator Node() const { 
+        return _index >= 0 ? _algorithm->_process[_index] : INVALID;
+      }
+
+      /// \brief Increment operator.
+      ///
+      /// Increment operator.
+      ActiveIt& operator++() {
+        --_index;
+        return *this; 
+      }
+
+      bool operator==(const ActiveIt& it) const { 
+        return static_cast<Node>(*this) == static_cast<Node>(it); 
+      }
+      bool operator!=(const ActiveIt& it) const { 
+        return static_cast<Node>(*this) != static_cast<Node>(it); 
+      }
+      bool operator<(const ActiveIt& it) const { 
+        return static_cast<Node>(*this) < static_cast<Node>(it); 
+      }
+      
+    private:
+      const BellmanFord* _algorithm;
+      int _index;
+    };
+    
+    /// \name Query Functions
+    /// The result of the Bellman-Ford algorithm can be obtained using these
+    /// functions.\n
+    /// Either \ref run() or \ref init() should be called before using them.
+    
+    ///@{
+
+    /// \brief The shortest path to the given node.
+    ///    
+    /// Gives back the shortest path to the given node from the root(s).
+    ///
+    /// \warning \c t should be reached from the root(s).
+    ///
+    /// \pre Either \ref run() or \ref init() must be called before
+    /// using this function.
+    Path path(Node t) const
+    {
+      return Path(*_gr, *_pred, t);
+    }
+	  
+    /// \brief The distance of the given node from the root(s).
+    ///
+    /// Returns the distance of the given node from the root(s).
+    ///
+    /// \warning If node \c v is not reached from the root(s), then
+    /// the return value of this function is undefined.
+    ///
+    /// \pre Either \ref run() or \ref init() must be called before
+    /// using this function.
+    Value dist(Node v) const { return (*_dist)[v]; }
+
+    /// \brief Returns the 'previous arc' of the shortest path tree for
+    /// the given node.
+    ///
+    /// This function returns the 'previous arc' of the shortest path
+    /// tree for node \c v, i.e. it returns the last arc of a
+    /// shortest path from a root to \c v. It is \c INVALID if \c v
+    /// is not reached from the root(s) or if \c v is a root.
+    ///
+    /// The shortest path tree used here is equal to the shortest path
+    /// tree used in \ref predNode() and \predMap().
+    ///
+    /// \pre Either \ref run() or \ref init() must be called before
+    /// using this function.
+    Arc predArc(Node v) const { return (*_pred)[v]; }
+
+    /// \brief Returns the 'previous node' of the shortest path tree for
+    /// the given node.
+    ///
+    /// This function returns the 'previous node' of the shortest path
+    /// tree for node \c v, i.e. it returns the last but one node of
+    /// a shortest path from a root to \c v. It is \c INVALID if \c v
+    /// is not reached from the root(s) or if \c v is a root.
+    ///
+    /// The shortest path tree used here is equal to the shortest path
+    /// tree used in \ref predArc() and \predMap().
+    ///
+    /// \pre Either \ref run() or \ref init() must be called before
+    /// using this function.
+    Node predNode(Node v) const { 
+      return (*_pred)[v] == INVALID ? INVALID : _gr->source((*_pred)[v]); 
+    }
+    
+    /// \brief Returns a const reference to the node map that stores the
+    /// distances of the nodes.
+    ///
+    /// Returns a const reference to the node map that stores the distances
+    /// of the nodes calculated by the algorithm.
+    ///
+    /// \pre Either \ref run() or \ref init() must be called before
+    /// using this function.
+    const DistMap &distMap() const { return *_dist;}
+ 
+    /// \brief Returns a const reference to the node map that stores the
+    /// predecessor arcs.
+    ///
+    /// Returns a const reference to the node map that stores the predecessor
+    /// arcs, which form the shortest path tree (forest).
+    ///
+    /// \pre Either \ref run() or \ref init() must be called before
+    /// using this function.
+    const PredMap &predMap() const { return *_pred; }
+ 
+    /// \brief Checks if a node is reached from the root(s).
+    ///
+    /// Returns \c true if \c v is reached from the root(s).
+    ///
+    /// \pre Either \ref run() or \ref init() must be called before
+    /// using this function.
+    bool reached(Node v) const {
+      return (*_dist)[v] != OperationTraits::infinity();
+    }
+
+    /// \brief Gives back a negative cycle.
+    ///    
+    /// This function gives back a directed cycle with negative total
+    /// length if the algorithm has already found one.
+    /// Otherwise it gives back an empty path.
+    lemon::Path<Digraph> negativeCycle() {
+      typename Digraph::template NodeMap<int> state(*_gr, -1);
+      lemon::Path<Digraph> cycle;
+      for (int i = 0; i < int(_process.size()); ++i) {
+        if (state[_process[i]] != -1) continue;
+        for (Node v = _process[i]; (*_pred)[v] != INVALID;
+             v = _gr->source((*_pred)[v])) {
+          if (state[v] == i) {
+            cycle.addFront((*_pred)[v]);
+            for (Node u = _gr->source((*_pred)[v]); u != v;
+                 u = _gr->source((*_pred)[u])) {
+              cycle.addFront((*_pred)[u]);
+            }
+            return cycle;
+          }
+          else if (state[v] >= 0) {
+            break;
+          }
+          state[v] = i;
+        }
+      }
+      return cycle;
+    }
+    
+    ///@}
+  };
+ 
+  /// \brief Default traits class of bellmanFord() function.
+  ///
+  /// Default traits class of bellmanFord() function.
+  /// \tparam GR The type of the digraph.
+  /// \tparam LEN The type of the length map.
+  template <typename GR, typename LEN>
+  struct BellmanFordWizardDefaultTraits {
+    /// The type of the digraph the algorithm runs on. 
+    typedef GR Digraph;
+
+    /// \brief The type of the map that stores the arc lengths.
+    ///
+    /// The type of the map that stores the arc lengths.
+    /// It must meet the \ref concepts::ReadMap "ReadMap" concept.
+    typedef LEN LengthMap;
+
+    /// The type of the arc lengths.
+    typedef typename LEN::Value Value;
+
+    /// \brief Operation traits for Bellman-Ford algorithm.
+    ///
+    /// It defines the used operations and the infinity value for the
+    /// given \c Value type.
+    /// \see BellmanFordDefaultOperationTraits
+    typedef BellmanFordDefaultOperationTraits<Value> OperationTraits;
+
+    /// \brief The type of the map that stores the last
+    /// arcs of the shortest paths.
+    /// 
+    /// The type of the map that stores the last arcs of the shortest paths.
+    /// It must conform to the \ref concepts::WriteMap "WriteMap" concept.
+    typedef typename GR::template NodeMap<typename GR::Arc> PredMap;
+
+    /// \brief Instantiates a \c PredMap.
+    /// 
+    /// This function instantiates a \ref PredMap.
+    /// \param g is the digraph to which we would like to define the
+    /// \ref PredMap.
+    static PredMap *createPredMap(const GR &g) {
+      return new PredMap(g);
+    }
+
+    /// \brief The type of the map that stores the distances of the nodes.
+    ///
+    /// The type of the map that stores the distances of the nodes.
+    /// It must conform to the \ref concepts::WriteMap "WriteMap" concept.
+    typedef typename GR::template NodeMap<Value> DistMap;
+
+    /// \brief Instantiates a \c DistMap.
+    ///
+    /// This function instantiates a \ref DistMap. 
+    /// \param g is the digraph to which we would like to define the
+    /// \ref DistMap.
+    static DistMap *createDistMap(const GR &g) {
+      return new DistMap(g);
+    }
+
+    ///The type of the shortest paths.
+
+    ///The type of the shortest paths.
+    ///It must meet the \ref concepts::Path "Path" concept.
+    typedef lemon::Path<Digraph> Path;
+  };
+  
+  /// \brief Default traits class used by BellmanFordWizard.
+  ///
+  /// Default traits class used by BellmanFordWizard.
+  /// \tparam GR The type of the digraph.
+  /// \tparam LEN The type of the length map.
+  template <typename GR, typename LEN>
+  class BellmanFordWizardBase 
+    : public BellmanFordWizardDefaultTraits<GR, LEN> {
+
+    typedef BellmanFordWizardDefaultTraits<GR, LEN> Base;
+  protected:
+    // Type of the nodes in the digraph.
+    typedef typename Base::Digraph::Node Node;
+
+    // Pointer to the underlying digraph.
+    void *_graph;
+    // Pointer to the length map
+    void *_length;
+    // Pointer to the map of predecessors arcs.
+    void *_pred;
+    // Pointer to the map of distances.
+    void *_dist;
+    //Pointer to the shortest path to the target node.
+    void *_path;
+    //Pointer to the distance of the target node.
+    void *_di;
+
+    public:
+    /// Constructor.
+    
+    /// This constructor does not require parameters, it initiates
+    /// all of the attributes to default values \c 0.
+    BellmanFordWizardBase() :
+      _graph(0), _length(0), _pred(0), _dist(0), _path(0), _di(0) {}
+
+    /// Constructor.
+    
+    /// This constructor requires two parameters,
+    /// others are initiated to \c 0.
+    /// \param gr The digraph the algorithm runs on.
+    /// \param len The length map.
+    BellmanFordWizardBase(const GR& gr, 
+			  const LEN& len) :
+      _graph(reinterpret_cast<void*>(const_cast<GR*>(&gr))), 
+      _length(reinterpret_cast<void*>(const_cast<LEN*>(&len))), 
+      _pred(0), _dist(0), _path(0), _di(0) {}
+
+  };
+  
+  /// \brief Auxiliary class for the function-type interface of the
+  /// \ref BellmanFord "Bellman-Ford" algorithm.
+  ///
+  /// This auxiliary class is created to implement the
+  /// \ref bellmanFord() "function-type interface" of the
+  /// \ref BellmanFord "Bellman-Ford" algorithm.
+  /// It does not have own \ref run() method, it uses the
+  /// functions and features of the plain \ref BellmanFord.
+  ///
+  /// This class should only be used through the \ref bellmanFord()
+  /// function, which makes it easier to use the algorithm.
+  template<class TR>
+  class BellmanFordWizard : public TR {
+    typedef TR Base;
+
+    typedef typename TR::Digraph Digraph;
+
+    typedef typename Digraph::Node Node;
+    typedef typename Digraph::NodeIt NodeIt;
+    typedef typename Digraph::Arc Arc;
+    typedef typename Digraph::OutArcIt ArcIt;
+    
+    typedef typename TR::LengthMap LengthMap;
+    typedef typename LengthMap::Value Value;
+    typedef typename TR::PredMap PredMap;
+    typedef typename TR::DistMap DistMap;
+    typedef typename TR::Path Path;
+
+  public:
+    /// Constructor.
+    BellmanFordWizard() : TR() {}
+
+    /// \brief Constructor that requires parameters.
+    ///
+    /// Constructor that requires parameters.
+    /// These parameters will be the default values for the traits class.
+    /// \param gr The digraph the algorithm runs on.
+    /// \param len The length map.
+    BellmanFordWizard(const Digraph& gr, const LengthMap& len) 
+      : TR(gr, len) {}
+
+    /// \brief Copy constructor
+    BellmanFordWizard(const TR &b) : TR(b) {}
+
+    ~BellmanFordWizard() {}
+
+    /// \brief Runs the Bellman-Ford algorithm from the given source node.
+    ///    
+    /// This method runs the Bellman-Ford algorithm from the given source
+    /// node in order to compute the shortest path to each node.
+    void run(Node s) {
+      BellmanFord<Digraph,LengthMap,TR> 
+	bf(*reinterpret_cast<const Digraph*>(Base::_graph), 
+           *reinterpret_cast<const LengthMap*>(Base::_length));
+      if (Base::_pred) bf.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
+      if (Base::_dist) bf.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
+      bf.run(s);
+    }
+
+    /// \brief Runs the Bellman-Ford algorithm to find the shortest path
+    /// between \c s and \c t.
+    ///
+    /// This method runs the Bellman-Ford algorithm from node \c s
+    /// in order to compute the shortest path to node \c t.
+    /// Actually, it computes the shortest path to each node, but using
+    /// this function you can retrieve the distance and the shortest path
+    /// for a single target node easier.
+    ///
+    /// \return \c true if \c t is reachable form \c s.
+    bool run(Node s, Node t) {
+      BellmanFord<Digraph,LengthMap,TR>
+        bf(*reinterpret_cast<const Digraph*>(Base::_graph),
+           *reinterpret_cast<const LengthMap*>(Base::_length));
+      if (Base::_pred) bf.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
+      if (Base::_dist) bf.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
+      bf.run(s);
+      if (Base::_path) *reinterpret_cast<Path*>(Base::_path) = bf.path(t);
+      if (Base::_di) *reinterpret_cast<Value*>(Base::_di) = bf.dist(t);
+      return bf.reached(t);
+    }
+
+    template<class T>
+    struct SetPredMapBase : public Base {
+      typedef T PredMap;
+      static PredMap *createPredMap(const Digraph &) { return 0; };
+      SetPredMapBase(const TR &b) : TR(b) {}
+    };
+    
+    /// \brief \ref named-templ-param "Named parameter" for setting
+    /// the predecessor map.
+    ///
+    /// \ref named-templ-param "Named parameter" for setting
+    /// the map that stores the predecessor arcs of the nodes.
+    template<class T>
+    BellmanFordWizard<SetPredMapBase<T> > predMap(const T &t) {
+      Base::_pred=reinterpret_cast<void*>(const_cast<T*>(&t));
+      return BellmanFordWizard<SetPredMapBase<T> >(*this);
+    }
+    
+    template<class T>
+    struct SetDistMapBase : public Base {
+      typedef T DistMap;
+      static DistMap *createDistMap(const Digraph &) { return 0; };
+      SetDistMapBase(const TR &b) : TR(b) {}
+    };
+    
+    /// \brief \ref named-templ-param "Named parameter" for setting
+    /// the distance map.
+    ///
+    /// \ref named-templ-param "Named parameter" for setting
+    /// the map that stores the distances of the nodes calculated
+    /// by the algorithm.
+    template<class T>
+    BellmanFordWizard<SetDistMapBase<T> > distMap(const T &t) {
+      Base::_dist=reinterpret_cast<void*>(const_cast<T*>(&t));
+      return BellmanFordWizard<SetDistMapBase<T> >(*this);
+    }
+
+    template<class T>
+    struct SetPathBase : public Base {
+      typedef T Path;
+      SetPathBase(const TR &b) : TR(b) {}
+    };
+
+    /// \brief \ref named-func-param "Named parameter" for getting
+    /// the shortest path to the target node.
+    ///
+    /// \ref named-func-param "Named parameter" for getting
+    /// the shortest path to the target node.
+    template<class T>
+    BellmanFordWizard<SetPathBase<T> > path(const T &t)
+    {
+      Base::_path=reinterpret_cast<void*>(const_cast<T*>(&t));
+      return BellmanFordWizard<SetPathBase<T> >(*this);
+    }
+
+    /// \brief \ref named-func-param "Named parameter" for getting
+    /// the distance of the target node.
+    ///
+    /// \ref named-func-param "Named parameter" for getting
+    /// the distance of the target node.
+    BellmanFordWizard dist(const Value &d)
+    {
+      Base::_di=reinterpret_cast<void*>(const_cast<Value*>(&d));
+      return *this;
+    }
+    
+  };
+  
+  /// \brief Function type interface for the \ref BellmanFord "Bellman-Ford"
+  /// algorithm.
+  ///
+  /// \ingroup shortest_path
+  /// Function type interface for the \ref BellmanFord "Bellman-Ford"
+  /// algorithm.
+  ///
+  /// This function also has several \ref named-templ-func-param 
+  /// "named parameters", they are declared as the members of class 
+  /// \ref BellmanFordWizard.
+  /// The following examples show how to use these parameters.
+  /// \code
+  ///   // Compute shortest path from node s to each node
+  ///   bellmanFord(g,length).predMap(preds).distMap(dists).run(s);
+  ///
+  ///   // Compute shortest path from s to t
+  ///   bool reached = bellmanFord(g,length).path(p).dist(d).run(s,t);
+  /// \endcode
+  /// \warning Don't forget to put the \ref BellmanFordWizard::run() "run()"
+  /// to the end of the parameter list.
+  /// \sa BellmanFordWizard
+  /// \sa BellmanFord
+  template<typename GR, typename LEN>
+  BellmanFordWizard<BellmanFordWizardBase<GR,LEN> >
+  bellmanFord(const GR& digraph,
+	      const LEN& length)
+  {
+    return BellmanFordWizard<BellmanFordWizardBase<GR,LEN> >(digraph, length);
+  }
+
+} //END OF NAMESPACE LEMON
+
+#endif
+