text: //
  //  Copyright (c) 2010 Athanasios Iliopoulos
  //
  //  Distributed under the Boost Software License, Version 1.0. (See
  //  accompanying file LICENSE_1_0.txt or copy at
  //  http://www.boost.org/LICENSE_1_0.txt)
  //
  
  #ifndef ASSIGNMENT_HPP
  #define ASSIGNMENT_HPP
  #include <boost/numeric/ublas/vector_expression.hpp>
  #include <boost/numeric/ublas/matrix_expression.hpp>
  
  /*! \file assignment.hpp
      \brief uBlas assignment operator <<=.
  */
  
  namespace boost { namespace numeric { namespace ublas {
  
  /** \brief A CRTP and Barton-Nackman trick index manipulator wrapper class.
   *
   * This class is not meant to be used directly.
   */
  template <class TV>
  class index_manipulator {
  public:
      typedef TV type;
      BOOST_UBLAS_INLINE
      const type &operator () () const {
          return *static_cast<const type *> (this);
      }
      BOOST_UBLAS_INLINE
      type &operator () () {
          return *static_cast<type *> (this);
      }
  };
  
  /** \brief A move_to vector index manipulator.
   *
   * When member function \c manip is called the referenced
   * index will be set to the manipulators' index.
   *
   * \sa move_to(T i)
   */
  template <typename T>
  class vector_move_to_manip: public index_manipulator<vector_move_to_manip<T> > {
  public:
      BOOST_UBLAS_INLINE
      vector_move_to_manip(const T &k): i(k) { }
  
      template <typename V>
      BOOST_UBLAS_INLINE
      void manip(V &k) const { k=i; }
  private:
      T i;
  };
  
  /** \brief An object generator that returns a move_to vector index manipulator
   *
   * \param i The element number the manipulator will move to when \c manip member function is called
   * \return A move_to vector manipulator
   *
   * Example usage:
   * \code
   * vector<double> a(6, 0);
   * a <<= 1, 2, move_to(5), 3;
   * \endcode
   * will result in:
   * \code
   * 1 2 0 0 0 3
   * \endcode
   *
   * \tparam T Size type
   * \sa move_to()
   */
  template <typename T>
  BOOST_UBLAS_INLINE vector_move_to_manip<T>  move_to(T i) {
      return vector_move_to_manip<T>(i);
  }
  
  /** \brief A static move to vector manipulator.
   *
   * When member function \c manip is called the referenced
   * index will be set to the manipulators' index
   *
   * \sa move_to(T i) and move_to()
  */
  template <std::size_t I>
  class static_vector_move_to_manip: public index_manipulator<static_vector_move_to_manip<I> > {
  public:
      template <typename V>
      BOOST_UBLAS_INLINE
      void manip(V &k) const { k=I; }
  };
  
  /** \brief An object generator that returns a static move_to vector index  manipulator.
   *
   * Typically faster than the dynamic version, but can be used only when the
   * values are known at compile time.
   *
   * \return A static move_to vector manipulator
   *
   * Example usage:
   * \code
   * vector<double> a(6, 0);
   * a <<= 1, 2, move_to<5>(), 3;
   * \endcode
   * will result in:
   * \code
   * 1 2 0 0 0 3
   * \endcode
   *
   * \tparam I The number of elements the manipulator will traverse the index when \c manip function is called
   */
  template <std::size_t I>
  BOOST_UBLAS_INLINE static_vector_move_to_manip<I>  move_to() {
      return static_vector_move_to_manip<I>();
  }
  
  /** \brief A move vector index manipulator.
   *
   * When member function traverse is called the manipulators'
   * index will be added to the referenced index.
   *
   * \see move(T i)
   */
  template <typename T>
  class vector_move_manip: public index_manipulator<vector_move_manip<T> > {
  public:
      BOOST_UBLAS_INLINE
      vector_move_manip(const T &k): i(k) { }
  
      template <typename V>
      BOOST_UBLAS_INLINE void manip(V &k) const { k+=i; }
  private:
      T i;
  };
  
  /**
  * \brief  An object generator that returns a move vector index manipulator
  *
  * \tparam T Size type
  * \param i The number of elements the manipulator will traverse the index when \c manip
  * member function is called. Negative values can be used.
  * \return A move vector manipulator
  *
  * Example usage:
  * \code
  * vector<double> a(6, 0);
  * a <<= 1, 2, move(3), 3;
  * \endcode
  * will result in:
  * \code
  * 1 2 0 0 0 3
  * \endcode
  *
  */
  template <typename T>
  BOOST_UBLAS_INLINE vector_move_manip<T>  move(T i) {
      return vector_move_manip<T>(i);
  }
  
  /**
  * \brief A static move vector manipulator
  *
  * When member function \c manip is called the manipulators
  * index will be added to the referenced index
  *
  * \sa move()
  *
  * \todo Doxygen has some problems with similar template functions. Correct that.
  */
  template <std::ptrdiff_t I>
  class static_vector_move_manip: public index_manipulator<static_vector_move_manip<I> > {
  public:
      template <typename V>
      BOOST_UBLAS_INLINE void manip(V &k) const { k+=I; }
  };
  
  /**
  * \brief An object generator that returns a static move vector index manipulator.
  *
  * Typically faster than the dynamic version, but can be used only when the
  * values are known at compile time.
  * \tparam I The Number of elements the manipulator will traverse the index when \c manip
  * function is called.Negative values can be used.
  * \return A static move vector manipulator
  *
  * Example usage:
  * \code
  * vector<double> a(6, 0);
  * a <<= 1, 2, move<3>(), 3;
  * \endcode
  * will result in:
  * \code
  * 1 2 0 0 0 3
  * \endcode
  *
  * \todo Doxygen has some problems with similar template functions. Correct that.
  */
  template <std::ptrdiff_t I>
  static_vector_move_manip<I>  move() {
      return static_vector_move_manip<I>();
  }
  
  /**
  * \brief A move_to matrix manipulator
  *
  * When member function \c manip is called the referenced
  * index will be set to the manipulators' index
  *
  * \sa move_to(T i, T j)
  *
  * \todo Doxygen has some problems with similar template functions. Correct that.
  */
  template <typename T>
  class matrix_move_to_manip: public index_manipulator<matrix_move_to_manip<T> > {
  public:
      BOOST_UBLAS_INLINE
      matrix_move_to_manip(T k, T l): i(k), j(l) { }
  
      template <typename V1, typename V2>
      BOOST_UBLAS_INLINE
      void manip(V1 &k, V2 &l) const {
          k=i;
          l=j;
      }
  private:
      T i, j;
  };
  
  /**
  * \brief  An object generator that returns a "move_to" matrix index manipulator
  *
  * \tparam size type
  * \param i The row number the manipulator will move to when \c manip
  * member function is called
  * \param j The column number the manipulator will move to when \c manip
  * member function is called
  * \return A move matrix manipulator
  *
  * Example usage:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, move_to(A.size1()-1, A.size1()-1), 3;
  * \endcode
  * will result in:
  * \code
  * 1 2 0
  * 0 0 0
  * 0 0 3
  * \endcode
  * \sa move_to(T i, T j) and static_matrix_move_to_manip
  *
  * \todo Doxygen has some problems with similar template functions. Correct that.
  */
  template <typename T>
  BOOST_UBLAS_INLINE matrix_move_to_manip<T>  move_to(T i, T j) {
      return matrix_move_to_manip<T>(i, j);
  }
  
  
  /**
  * \brief A static move_to matrix manipulator
  * When member function traverse is called the referenced
  * index will be set to the manipulators' index
  *
  * \sa move_to()
  *
  * \todo Doxygen has some problems with similar template functions. Correct that.
  */
  template <std::size_t I,std::size_t J>
  class static_matrix_move_to_manip: public index_manipulator<static_matrix_move_to_manip<I, J> > {
  public:
      template <typename V, typename K>
      BOOST_UBLAS_INLINE
      void manip(V &k, K &l) const {
          k=I;
          l=J;
      }
  };
  
  /**
  * \brief  An object generator that returns a static move_to matrix index manipulator.
  *
  * Typically faster than the dynamic version, but can be used only when the
  * values are known at compile time.
  * \tparam I The row number the manipulator will set the matrix assigner index to.
  * \tparam J The column number the manipulator will set the matrix assigner index to.
  * \return A static move_to matrix manipulator
  *
  * Example usage:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, move_to<2,2>, 3;
  * \endcode
  * will result in:
  * \code
  * 1 2 0
  * 0 0 0
  * 0 0 3
  * \endcode
  * \sa move_to(T i, T j) and static_matrix_move_to_manip
  */
  template <std::size_t I, std::size_t J>
  BOOST_UBLAS_INLINE static_matrix_move_to_manip<I, J>  move_to() {
      return static_matrix_move_to_manip<I, J>();
  }
  
  /**
  * \brief A move matrix index manipulator.
  *
  * When member function \c manip is called the manipulator's
  * index will be added to the referenced' index.
  *
  * \sa move(T i, T j)
  */
  template <typename T>
  class matrix_move_manip: public index_manipulator<matrix_move_manip<T> > {
  public:
      BOOST_UBLAS_INLINE
      matrix_move_manip(T k, T l): i(k), j(l) { }
  
      template <typename V, typename K>
      BOOST_UBLAS_INLINE
      void manip(V &k, K &l) const {
          k+=i;
          l+=j;
      }
  private:
      T i, j;
  };
  
  /**
  * \brief  An object generator that returns a move matrix index manipulator
  *
  * \tparam size type
  * \param i The number of rows the manipulator will traverse the index when "manip"
  * member function is called
  * \param j The number of columns the manipulator will traverse the index when "manip"
  * member function is called
  * \return A move matrix manipulator
  *
  * Example:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, move(1,0),
  *            3,;
  * \endcode
  * will result in:
  * \code
  * 1 2 0
  * 0 0 3
  * 0 0 0
  * \endcode
  */
  template <typename T>
  BOOST_UBLAS_INLINE matrix_move_manip<T>  move(T i, T j) {
      return matrix_move_manip<T>(i, j);
  }
  
  /**
  * \brief A static move matrix index manipulator.
  *
  * When member function traverse is called the manipulator's
  * index will be added to the referenced' index.
  *
  * \sa move()
  *
  * \todo Doxygen has some problems with similar template functions. Correct that.
  */
  template <std::ptrdiff_t I, std::ptrdiff_t J>
  class static_matrix_move_manip: public index_manipulator<static_matrix_move_manip<I, J> > {
  public:
      template <typename V, typename K>
      BOOST_UBLAS_INLINE
      void manip(V &k, K &l) const {
          k+=I;
          l+=J;
      }
  };
  
  /**
  * \brief  An object generator that returns a static "move" matrix index manipulator.
  *
  * Typically faster than the dynamic version, but can be used only when the
  * values are known at compile time. Negative values can be used.
  * \tparam I The number of rows the manipulator will trasverse the matrix assigner index.
  * \tparam J The number of columns the manipulator will trasverse the matrix assigner index.
  * \tparam size type
  * \return A static move matrix manipulator
  *
  * Example:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, move<1,0>(),
  *            3,;
  * \endcode
  * will result in:
  * \code
  * 1 2 0
  * 0 0 3
  * 0 0 0
  * \endcode
  *
  * \sa move_to()
  *
  * \todo Doxygen has some problems with similar template functions. Correct that.
  */
  template <std::ptrdiff_t I, std::ptrdiff_t J>
  BOOST_UBLAS_INLINE static_matrix_move_manip<I, J>  move() {
      return static_matrix_move_manip<I, J>();
  }
  
  /**
  * \brief A begining of row manipulator
  *
  * When member function \c manip is called the referenced
  * index will be be set to the begining of the row (i.e. column = 0)
  *
  * \sa begin1()
  */
  class begin1_manip: public index_manipulator<begin1_manip > {
  public:
      template <typename V, typename K>
      BOOST_UBLAS_INLINE
      void manip(V & k, K &/*l*/) const {
          k=0;
      }
  };
  
  /**
  * \brief  An object generator that returns a begin1 manipulator.
  *
  * The resulted manipulator will traverse the index to the begining
  * of the current column when its' \c manip member function is called.
  *
  * \return A begin1 matrix index manipulator
  *
  * Example usage:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, next_row(),
  *      3, 4, begin1(), 1;
  * \endcode
  * will result in:
  * \code
  * 1 2 1
  * 3 4 0
  * 0 0 0
  * \endcode
  * \sa begin2()
  */
  inline begin1_manip  begin1() {
      return begin1_manip();
  }
  
  /**
  * \brief A begining of column manipulator
  *
  * When member function \c manip is called the referenced
  * index will be be set to the begining of the column (i.e. row = 0).
  *
  *
  * \sa begin2()
  */
  class begin2_manip: public index_manipulator<begin2_manip > {
  public:
      template <typename V, typename K>
      BOOST_UBLAS_INLINE
      void manip(V &/*k*/, K &l) const {
          l=0;
      }
  };
  
  /**
  * \brief  An object generator that returns a begin2 manipulator to be used to traverse a matrix.
  *
  * The resulted manipulator will traverse the index to the begining
  * of the current row when its' \c manip member function is called.
  *
  * \return A begin2 matrix manipulator
  *
  * Example:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, move<1,0>(),
  *      3, begin2(), 1;
  * \endcode
  * will result in:
  * \code
  * 1 2 0
  * 1 0 3
  * 0 0 0
  * \endcode
  * \sa begin1() begin2_manip
  */
  inline begin2_manip  begin2() {
      return begin2_manip();
  }
  
  
  /**
  * \brief A next row matrix manipulator.
  *
  * When member function traverse is called the referenced
  * index will be traveresed to the begining of next row.
  *
  * \sa next_row()
  */
  class next_row_manip: public index_manipulator<next_row_manip> {
  public:
      template <typename V, typename K>
      BOOST_UBLAS_INLINE
      void manip(V &k, K &l) const {
          k++;
          l=0;
      }
  };
  
  /**
  * \brief  An object generator that returns a next_row manipulator.
  *
  * The resulted manipulator will traverse the index to the begining
  * of the next row when it's manip member function is called.
  *
  * \return A next_row matrix manipulator.
  *
  * Example:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, next_row(),
  *      3, 4;
  * \endcode
  * will result in:
  * \code
  * 1 2 0
  * 3 4 0
  * 0 0 0
  * \endcode
  * \sa next_column()
  */
  inline next_row_manip  next_row() {
      return next_row_manip();
  }
  
  /**
  * \brief A next column matrix manipulator.
  *
  * When member function traverse is called the referenced
  * index will be traveresed to the begining of next column.
  *
  * \sa next_column()
  */
  class next_column_manip: public index_manipulator<next_column_manip> {
  public:
      template <typename V, typename K>
      BOOST_UBLAS_INLINE
      void manip(V &k, K &l) const {
          k=0;
          l++;
      }
  };
  
  /**
  * \brief  An object generator that returns a next_row manipulator.
  *
  * The resulted manipulator will traverse the index to the begining
  * of the next column when it's manip member function is called.
  *
  * \return A next_column matrix manipulator.
  *
  * Example:
  * \code:
  * matrix<double> A(3, 3, 0);
  * A <<= 1, 2, 0,
  *      3, next_column(), 4;
  * \endcode
  * will result in:
  * \code
  * 1 2 4
  * 3 0 0
  * 0 0 0
  * \endcode
  *
  */
  inline next_column_manip next_column() {
      return next_column_manip();
  }
  
  /**
  * \brief  A wrapper for fill policy classes
  *
  */
  template <class T>
  class fill_policy_wrapper {
  public:
      typedef T type;
  };
  
  // Collection of the fill policies
  namespace fill_policy {
  
      /**
      * \brief  An index assign policy
      *
      * This policy is used to for the simplified ublas assign through
      * normal indexing.
      *
      *
      */
      class index_assign :public fill_policy_wrapper<index_assign> {
      public:
          template <class T, typename S, typename V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const V &v) {
              e()(i) = v;
          }
          template <class T, typename S, typename V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const S &j, const V &v) {
              e()(i, j) = v;
          }
      };
  
      /**
      * \brief  An index plus assign policy
      *
      * This policy is used when the assignment is desired to be followed
      * by an addition.
      *
      *
      */
      class index_plus_assign :public fill_policy_wrapper<index_plus_assign> {
      public:
          template <class T, typename S, typename V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const V &v) {
              e()(i) += v;
          }
          template <class T, typename S, typename V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const S &j, const V &v) {
              e()(i, j) += v;
          }
      };
  
      /**
      * \brief  An index minus assign policy
      *
      * This policy is used when the assignment is desired to be followed
      * by a substraction.
      *
      *
      */
      class index_minus_assign :public fill_policy_wrapper<index_minus_assign> {
      public:
          template <class T, typename S, typename V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const V &v) {
              e()(i) -= v;
          }
          template <class T, typename S, typename V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const S &j, const V &v) {
              e()(i, j) -= v;
          }
      };
  
      /**
      * \brief  The sparse push_back fill policy.
      *
      * This policy is adequate for sparse types, when fast filling is required, where indexing
      * assign is pretty slow.
  
      * It is important to note that push_back assign cannot be used to add elements before elements
      * already existing in a sparse container. To achieve that please use the sparse_insert fill policy.
      */
      class sparse_push_back :public fill_policy_wrapper<sparse_push_back > {
      public:
          template <class T, class S, class V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const V &v) {
              e().push_back(i, v);
          }
          template <class T, class S, class V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const S &j, const V &v) {
              e().push_back(i,j, v);
          }
      };
  
      /**
      * \brief  The sparse insert fill policy.
      *
      * This policy is adequate for sparse types, when fast filling is required, where indexing
      * assign is pretty slow. It is slower than sparse_push_back fill policy, but it can be used to
      * insert elements anywhere inside the container.
      */
      class sparse_insert :public fill_policy_wrapper<sparse_insert> {
      public:
          template <class T, class S, class V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const V &v) {
              e().insert_element(i, v);
          }
          template <class T, class S, class V>
          BOOST_UBLAS_INLINE
          static void apply(T &e, const S &i, const S &j, const V &v) {
              e().insert_element(i,j, v);
          }
      };
  
  }
  
  /** \brief A wrapper for traverse policy classes
  *
  */
  template <class T>
  class traverse_policy_wrapper {
  public:
      typedef T type;
  };
  
  // Collection of the traverse policies
  namespace traverse_policy {
  
  
      /**
      * \brief  The no wrap policy.
      *
      * The no wrap policy does not allow wrapping when assigning to a matrix
      */
      struct no_wrap {
          /**
          * \brief  Element wrap method
          */
          template <class S1, class S2, class S3>
          BOOST_UBLAS_INLINE
          static void apply1(const S1 &/*s*/, S2 &/*i*/, S3 &/*j*/) {
          }
  
          /**
          * \brief  Matrix block wrap method
          */
          template <class S1, class S2, class S3>
          BOOST_UBLAS_INLINE
          static void apply2(const S1 &/*s1*/, const S1 &/*s2*/, S2 &/*i1*/, S3 &/*i2*/) {
          }
      };
  
      /**
      * \brief  The wrap policy.
      *
      * The wrap policy enables element wrapping when assigning to a matrix
      */
      struct wrap {
          /**
          * \brief  Element wrap method
          */
          template <class S1, class S2, class S3>
          BOOST_UBLAS_INLINE
          static void apply1(const S1 &s, S2 &i1, S3 &i2) {
              if (i2>=s) {
                  i1++;
                  i2=0;
              }
          }
  
          /**
          * \brief  Matrix block wrap method
          */
          template <class S1, class S2, class S3>
          BOOST_UBLAS_INLINE
          static void apply2(const S1 &s1, const S1 &s2, S2 &i1, S3 &i2) {
              if (i2>=s2) i2=0;   // Wrap to the next block
              else i1-=s1;        // Move up (or right) one block
          }
      };
  
      /**
      * \brief  The row_by_row traverse policy
      *
      * This policy is used when the assignment is desired to happen
      * row_major wise for performance or other reasons.
      *
      * This is the default behaviour. To change it globally please define BOOST_UBLAS_DEFAULT_ASSIGN_BY_COLUMN
      * in the compilation options or in an adequate header file.
      *
      * Please see EXAMPLES_LINK for usage information.
      *
      * \todo Add examples link
      */
      template <class Wrap = wrap>
      class by_row_policy :public traverse_policy_wrapper<by_row_policy<Wrap> > {
      public:
          template <typename S1, typename S2>
          BOOST_UBLAS_INLINE
          static void advance(S1 &/*i*/, S2 &j) { j++;}
  
          template <class E1, class E2, typename S1, typename S2, typename S3, typename S4, typename S5>
          BOOST_UBLAS_INLINE
          static bool next(const E1 &e, const E2 &me, S1 &i, S2 &j, const S3 &/*i0*/, const S3 &j0, S4 &k, S5 &l) {
              l++; j++;
              if (l>=e().size2()) {
                  l=0; k++; j=j0; i++;
                  // It is assumed that the iteration starts from 0 and progresses only using this function from within
                  // an assigner object.
                  // Otherwise (i.e. if it is called outside the assigner object) apply2 should have been
                  // outside the if statement.
                  if (k>=e().size1()) {
                      j=j0+e().size2();
                      Wrap::apply2(e().size1(), me().size2(), i, j);
                      return false;
                  }
              }
              return true;
          }
  
          template <class E, typename S1, typename S2>
          BOOST_UBLAS_INLINE
          static void apply_wrap(const E& e, S1 &i, S2 &j) {
              Wrap::apply1(e().size2(), i, j);
          }
      };
  
      /**
      * \brief  The column_by_column traverse policy
      *
      * This policy is used when the assignment is desired to happen
      * column_major wise, for performance or other reasons.
      *
      * This is the NOT the default behaviour. To set this as the default define BOOST_UBLAS_DEFAULT_ASSIGN_BY_COLUMN
      * in the compilation options or in an adequate header file.
      *
      * Please see EXAMPLES_LINK for usage information.
      *
      * \todo Add examples link
      */
      template <class Wrap = wrap>
      class by_column_policy :public traverse_policy_wrapper<by_column_policy<Wrap> > {
      public:
          template <typename S1, typename S2>
          BOOST_UBLAS_INLINE
          static void advance(S1 &i, S2 &/*j*/) { i++;}
  
          template <class E1, class E2, typename S1, typename S2, typename S3, typename S4, typename S5>
          BOOST_UBLAS_INLINE
          static bool next(const E1 &e, const E2 &me, S1 &i, S2 &j, const S3 &i0, const S3 &/*j0*/, S4 &k, S5 &l) {
              k++; i++;
              if (k>=e().size1()) {
                  k=0; l++; i=i0; j++;
                  // It is assumed that the iteration starts from 0 and progresses only using this function from within
                  // an assigner object.
                  // Otherwise (i.e. if it is called outside the assigner object) apply2 should have been
                  // outside the if statement.
                  if (l>=e().size2()) {
                      i=i0+e().size1();
                      Wrap::apply2(e().size2(), me().size1(), j, i);
                      return false;
                  }
              }
              return true;
          }
  
          template <class E, typename S1, typename S2>
          BOOST_UBLAS_INLINE
          static void apply_wrap(const E& e, S1 &i, S2 &j) {
              Wrap::apply1(e().size1(), j, i);
          }
      };
  }
  #ifndef BOOST_UBLAS_DEFAULT_NO_WRAP_POLICY
      typedef traverse_policy::wrap DEFAULT_WRAP_POLICY;
  #else
      typedef traverse_policy::no_wrap DEFAULT_WRAP_POLICY;
  #endif
  
  #ifndef BOOST_UBLAS_DEFAULT_ASSIGN_BY_COLUMN
      typedef traverse_policy::by_row_policy<DEFAULT_WRAP_POLICY> DEFAULT_TRAVERSE_POLICY;
  #else
      typedef traverse_policy::by_column<DEFAULT_WRAP_POLICY> DEFAULT_TRAVERSE_POLICY;
  #endif
  
   // Traverse policy namespace
  namespace traverse_policy {
  
      inline by_row_policy<DEFAULT_WRAP_POLICY> by_row() {
      return by_row_policy<DEFAULT_WRAP_POLICY>();
      }
  
      inline by_row_policy<wrap> by_row_wrap() {
          return by_row_policy<wrap>();
      }
  
      inline by_row_policy<no_wrap> by_row_no_wrap() {
          return by_row_policy<no_wrap>();
      }
  
      inline by_column_policy<DEFAULT_WRAP_POLICY> by_column() {
          return by_column_policy<DEFAULT_WRAP_POLICY>();
      }
  
      inline by_column_policy<wrap> by_column_wrap() {
          return by_column_policy<wrap>();
      }
  
      inline by_column_policy<no_wrap> by_column_no_wrap() {
          return by_column_policy<no_wrap>();
      }
  
  }
  
  /**
  * \brief  An assigner object used to fill a vector using operator <<= and operator, (comma)
  *
  * This object is meant to be created by appropriate object generators.
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E, class Fill_Policy = fill_policy::index_assign>
  class vector_expression_assigner {
  public:
      typedef typename E::expression_type::value_type value_type;
      typedef typename E::expression_type::size_type size_type;
  
      BOOST_UBLAS_INLINE
      vector_expression_assigner(E &e):ve(e), i(0) {
      }
  
      BOOST_UBLAS_INLINE
      vector_expression_assigner(size_type k, E &e):ve(e), i(k) {
          // Overloaded like that so it can be differentiated from (E, val).
          // Otherwise there would be an ambiquity when value_type == size_type.
      }
  
      BOOST_UBLAS_INLINE
      vector_expression_assigner(E &e, value_type val):ve(e), i(0) {
          operator,(val);
      }
  
      template <class AE>
      BOOST_UBLAS_INLINE
      vector_expression_assigner(E &e, const vector_expression<AE> &nve):ve(e), i(0) {
          operator,(nve);
      }
  
      template <typename T>
      BOOST_UBLAS_INLINE
      vector_expression_assigner(E &e, const index_manipulator<T> &ta):ve(e), i(0) {
          operator,(ta);
      }
  
      BOOST_UBLAS_INLINE
      vector_expression_assigner &operator, (const value_type& val) {
          apply(val);
          return *this;
      }
  
      template <class AE>
      BOOST_UBLAS_INLINE
      vector_expression_assigner &operator, (const vector_expression<AE> &nve) {
          for (typename AE::size_type k = 0; k!= nve().size(); k++)
              operator,(nve()(k));
          return *this;
      }
  
      template <typename T>
      BOOST_UBLAS_INLINE
      vector_expression_assigner &operator, (const index_manipulator<T> &ta) {
          ta().manip(i);
          return *this;
      }
  
      template <class T>
      BOOST_UBLAS_INLINE
      vector_expression_assigner<E, T> operator, (fill_policy_wrapper<T>) const {
          return vector_expression_assigner<E, T>(i, ve);
      }
  
  private:
      BOOST_UBLAS_INLINE
      vector_expression_assigner &apply(const typename E::expression_type::value_type& val) {
          Fill_Policy::apply(ve, i++, val);
          return *this;
      }
  
  private:
      E &ve;
      size_type i;
  };
  
  /*
  // The following static assigner is about 30% slower than the dynamic one, probably due to the recursive creation of assigner objects.
  // It remains commented here for future reference.
  
  template <class E, std::size_t I=0>
  class static_vector_expression_assigner {
  public:
      typedef typename E::expression_type::value_type value_type;
      typedef typename E::expression_type::size_type size_type;
  
      BOOST_UBLAS_INLINE
      static_vector_expression_assigner(E &e):ve(e) {
      }
  
      BOOST_UBLAS_INLINE
      static_vector_expression_assigner(E &e, value_type val):ve(e) {
          operator,(val);
      }
  
      BOOST_UBLAS_INLINE
      static_vector_expression_assigner<E, I+1> operator, (const value_type& val) {
          return apply(val);
      }
  
  private:
      BOOST_UBLAS_INLINE
      static_vector_expression_assigner<E, I+1> apply(const typename E::expression_type::value_type& val) {
          ve()(I)=val;
          return static_vector_expression_assigner<E, I+1>(ve);
      }
  
  private:
      E &ve;
  };
  
  template <class E>
  BOOST_UBLAS_INLINE
  static_vector_expression_assigner<vector_expression<E>, 1 > test_static(vector_expression<E> &v, const typename E::value_type &val) {
      v()(0)=val;
      return static_vector_expression_assigner<vector_expression<E>, 1 >(v);
  }
  */
  
  
  /**
  * \brief  A vector_expression_assigner generator used with operator<<= for simple types
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E>
  BOOST_UBLAS_INLINE
  vector_expression_assigner<vector_expression<E> > operator<<=(vector_expression<E> &v, const typename E::value_type &val) {
      return vector_expression_assigner<vector_expression<E> >(v,val);
  }
  
  /**
  * \brief  ! A vector_expression_assigner generator used with operator<<= for vector expressions
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E1, class E2>
  BOOST_UBLAS_INLINE
  vector_expression_assigner<vector_expression<E1> > operator<<=(vector_expression<E1> &v, const vector_expression<E2> &ve) {
      return vector_expression_assigner<vector_expression<E1> >(v,ve);
  }
  
  /**
  * \brief  A vector_expression_assigner generator used with operator<<= for traverse manipulators
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E, typename T>
  BOOST_UBLAS_INLINE
  vector_expression_assigner<vector_expression<E> > operator<<=(vector_expression<E> &v, const index_manipulator<T> &nv) {
      return vector_expression_assigner<vector_expression<E> >(v,nv);
  }
  
  /**
  * \brief  A vector_expression_assigner generator used with operator<<= for choice of fill policy
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E, typename T>
  BOOST_UBLAS_INLINE
  vector_expression_assigner<vector_expression<E>, T> operator<<=(vector_expression<E> &v, fill_policy_wrapper<T>) {
      return vector_expression_assigner<vector_expression<E>, T>(v);
  }
  
  /**
  * \brief  An assigner object used to fill a vector using operator <<= and operator, (comma)
  *
  * This object is meant to be created by appropriate object generators.
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E, class Fill_Policy = fill_policy::index_assign, class Traverse_Policy = DEFAULT_TRAVERSE_POLICY >
  class matrix_expression_assigner {
  public:
      typedef typename E::expression_type::size_type size_type;
  
      BOOST_UBLAS_INLINE
      matrix_expression_assigner(E &e): me(e), i(0), j(0) {
      }
  
      BOOST_UBLAS_INLINE
      matrix_expression_assigner(E &e, size_type k, size_type l): me(e), i(k), j(l) {
      }
  
      BOOST_UBLAS_INLINE
      matrix_expression_assigner(E &e, typename E::expression_type::value_type val): me(e), i(0), j(0) {
          operator,(val);
      }
  
      template <class AE>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner(E &e, const vector_expression<AE> &nve):me(e), i(0), j(0) {
          operator,(nve);
      }
  
      template <class AE>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner(E &e, const matrix_expression<AE> &nme):me(e), i(0), j(0) {
          operator,(nme);
      }
  
      template <typename T>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner(E &e, const index_manipulator<T> &ta):me(e), i(0), j(0) {
          operator,(ta);
      }
  
      BOOST_UBLAS_INLINE
      matrix_expression_assigner &operator, (const typename E::expression_type::value_type& val) {
          Traverse_Policy::apply_wrap(me, i ,j);
          return apply(val);
      }
  
      template <class AE>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner &operator, (const vector_expression<AE> &nve) {
          for (typename AE::size_type k = 0; k!= nve().size(); k++) {
              operator,(nve()(k));
          }
          return *this;
      }
  
      template <class AE>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner &operator, (const matrix_expression<AE> &nme) {
          return apply(nme);
      }
  
      template <typename T>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner &operator, (const index_manipulator<T> &ta) {
          ta().manip(i, j);
          return *this;
      } 
  
      template <class T>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner<E, T, Traverse_Policy> operator, (fill_policy_wrapper<T>) const {
          return matrix_expression_assigner<E, T, Traverse_Policy>(me, i, j);
      }
  
  
      template <class T>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner<E, Fill_Policy, T> operator, (traverse_policy_wrapper<T>) {
          Traverse_Policy::apply_wrap(me, i ,j);
          return matrix_expression_assigner<E, Fill_Policy, T>(me, i, j);
      }
  
  private:
      BOOST_UBLAS_INLINE
      matrix_expression_assigner &apply(const typename E::expression_type::value_type& val) {
          Fill_Policy::apply(me, i, j, val);
          Traverse_Policy::advance(i,j);
          return *this;
      }
  
      template <class AE>
      BOOST_UBLAS_INLINE
      matrix_expression_assigner &apply(const matrix_expression<AE> &nme) {
          size_type bi = i;
          size_type bj = j;
          typename AE::size_type k=0, l=0;
          Fill_Policy::apply(me, i, j, nme()(k, l));
          while (Traverse_Policy::next(nme, me, i, j, bi, bj, k, l))
              Fill_Policy::apply(me, i, j, nme()(k, l));
          return *this;
      }
  
  private:
      E &me;
      size_type i, j;
  };
  
  /**
  * \brief  A matrix_expression_assigner generator used with operator<<= for simple types
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E>
  BOOST_UBLAS_INLINE
  matrix_expression_assigner<matrix_expression<E> > operator<<=(matrix_expression<E> &me, const typename E::value_type &val) {
      return matrix_expression_assigner<matrix_expression<E> >(me,val);
  }
  
  /**
  * \brief  A matrix_expression_assigner generator used with operator<<= for choice of fill policy
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E, typename T>
  BOOST_UBLAS_INLINE
  matrix_expression_assigner<matrix_expression<E>, T> operator<<=(matrix_expression<E> &me, fill_policy_wrapper<T>) {
      return matrix_expression_assigner<matrix_expression<E>, T>(me);
  }
  
  /**
  * \brief  A matrix_expression_assigner generator used with operator<<= for traverse manipulators
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E, typename T>
  BOOST_UBLAS_INLINE
  matrix_expression_assigner<matrix_expression<E> > operator<<=(matrix_expression<E> &me, const index_manipulator<T> &ta) {
      return matrix_expression_assigner<matrix_expression<E> >(me,ta);
  }
  
  /**
  * \brief  A matrix_expression_assigner generator used with operator<<= for traverse manipulators
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E, typename T>
  BOOST_UBLAS_INLINE
  matrix_expression_assigner<matrix_expression<E>, fill_policy::index_assign, T> operator<<=(matrix_expression<E> &me, traverse_policy_wrapper<T>) {
      return matrix_expression_assigner<matrix_expression<E>, fill_policy::index_assign, T>(me);
  }
  
  /**
  * \brief  A matrix_expression_assigner generator used with operator<<= for vector expressions
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E1, class E2>
  BOOST_UBLAS_INLINE
  matrix_expression_assigner<matrix_expression<E1> > operator<<=(matrix_expression<E1> &me, const vector_expression<E2> &ve) {
      return matrix_expression_assigner<matrix_expression<E1> >(me,ve);
  }
  
  /**
  * \brief  A matrix_expression_assigner generator used with operator<<= for matrix expressions
  *
  * Please see EXAMPLES_LINK for usage information.
  *
  * \todo Add examples link
  */
  template <class E1, class E2>
  BOOST_UBLAS_INLINE
  matrix_expression_assigner<matrix_expression<E1> > operator<<=(matrix_expression<E1> &me1, const matrix_expression<E2> &me2) {
      return matrix_expression_assigner<matrix_expression<E1> >(me1,me2);
  }
  
  } } }
  
  #endif // ASSIGNMENT_HPP
  