text: //=================================================================================================
  /*!
  //  \file blaze/math/adaptors/unilowermatrix/UniLowerElement.h
  //  \brief Header file for the UniLowerElement class
  //
  //  Copyright (C) 2012-2018 Klaus Iglberger - All Rights Reserved
  //
  //  This file is part of the Blaze library. You can redistribute it and/or modify it under
  //  the terms of the New (Revised) BSD License. Redistribution and use in source and binary
  //  forms, with or without modification, are permitted provided that the following conditions
  //  are met:
  //
  //  1. Redistributions of source code must retain the above copyright notice, this list of
  //     conditions and the following disclaimer.
  //  2. Redistributions in binary form must reproduce the above copyright notice, this list
  //     of conditions and the following disclaimer in the documentation and/or other materials
  //     provided with the distribution.
  //  3. Neither the names of the Blaze development group nor the names of its contributors
  //     may be used to endorse or promote products derived from this software without specific
  //     prior written permission.
  //
  //  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
  //  EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  //  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
  //  SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  //  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
  //  TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
  //  BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  //  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  //  ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
  //  DAMAGE.
  */
  //=================================================================================================
  
  #ifndef _BLAZE_MATH_ADAPTORS_UNILOWERMATRIX_UNILOWERELEMENT_H_
  #define _BLAZE_MATH_ADAPTORS_UNILOWERMATRIX_UNILOWERELEMENT_H_
  
  
  //*************************************************************************************************
  // Includes
  //*************************************************************************************************
  
  #include "../../../math/Aliases.h"
  #include "../../../math/adaptors/unilowermatrix/UniLowerValue.h"
  #include "../../../math/constraints/Expression.h"
  #include "../../../math/constraints/Hermitian.h"
  #include "../../../math/constraints/Lower.h"
  #include "../../../math/constraints/SparseMatrix.h"
  #include "../../../math/constraints/Symmetric.h"
  #include "../../../math/constraints/Upper.h"
  #include "../../../math/Exception.h"
  #include "../../../math/sparse/SparseElement.h"
  #include "../../../util/constraints/Const.h"
  #include "../../../util/constraints/Numeric.h"
  #include "../../../util/constraints/Pointer.h"
  #include "../../../util/constraints/Reference.h"
  #include "../../../util/constraints/Volatile.h"
  #include "../../../util/Types.h"
  
  
  namespace blaze {
  
  //=================================================================================================
  //
  //  CLASS DEFINITION
  //
  //=================================================================================================
  
  //*************************************************************************************************
  /*!\brief Representation of an element within a sparse lower unitriangular matrix.
  // \ingroup unilower_matrix
  //
  // The UniLowerElement class represents an element (i.e. value/index pair) within a sparse lower
  // unitriangular matrix. It guarantees that the unilower matrix invariant is not violated, i.e.
  // that elements in the upper part of the matrix remain 0 and the diagonal elements remain 1. The
  // following example illustrates this by means of a \f$ 3 \times 3 \f$ sparse lower unitriangular
  // matrix:
  
     \code
     using UniLower = blaze::UniLowerMatrix< blaze::CompressedMatrix<int> >;
  
     // Creating a 3x3 lower unitriangular sparse matrix
     UniLower A( 3UL );
  
     A(1,0) = -2;  //        (  1 0 0 )
     A(2,0) =  3;  // => A = ( -2 1 0 )
     A(2,1) =  5;  //        (  3 5 1 )
  
     UniLower::Iterator it = A.begin( 1UL );
     *it = 4;  // Modification of matrix element (1,0)
     ++it;
     *it = 9;  // Invalid assignment to diagonal matrix element; results in an exception!
     \endcode
  */
  template< typename MT >  // Type of the adapted matrix
  class UniLowerElement
     : private SparseElement
  {
   private:
     //**Type definitions****************************************************************************
     using ElementType  = ElementType_t<MT>;  //!< Type of the represented matrix element.
     using IteratorType = Iterator_t<MT>;     //!< Type of the underlying sparse matrix iterators.
     //**********************************************************************************************
  
   public:
     //**Type definitions****************************************************************************
     using ValueType      = UniLowerValue<MT>;        //!< The value type of the value-index-pair.
     using IndexType      = size_t;                   //!< The index type of the value-index-pair.
     using Reference      = UniLowerValue<MT>;        //!< Reference return type.
     using ConstReference = const UniLowerValue<MT>;  //!< Reference-to-const return type.
     using Pointer        = UniLowerElement*;         //!< Pointer return type.
     //**********************************************************************************************
  
     //**Constructor*********************************************************************************
     /*!\name Constructors */
     //@{
     inline UniLowerElement( IteratorType pos, bool diagonal );
     //@}
     //**********************************************************************************************
  
     //**Assignment operators************************************************************************
     /*!\name Assignment operators */
     //@{
     template< typename T > inline UniLowerElement& operator= ( const T& v );
     template< typename T > inline UniLowerElement& operator+=( const T& v );
     template< typename T > inline UniLowerElement& operator-=( const T& v );
     template< typename T > inline UniLowerElement& operator*=( const T& v );
     template< typename T > inline UniLowerElement& operator/=( const T& v );
     //@}
     //**********************************************************************************************
  
     //**Access operators****************************************************************************
     /*!\name Access operators */
     //@{
     inline Pointer operator->() noexcept;
     //@}
     //**********************************************************************************************
  
     //**Utility functions***************************************************************************
     /*!\name Utility functions */
     //@{
     inline Reference value() const;
     inline IndexType index() const;
     //@}
     //**********************************************************************************************
  
   private:
     //**Member variables****************************************************************************
     IteratorType pos_;  //!< Iterator to the current lower unitriangular matrix element.
     bool    diagonal_;  //!< \a true in case the element is on the diagonal, \a false if not.
     //**********************************************************************************************
  
     //**Compile time checks*************************************************************************
     /*! \cond BLAZE_INTERNAL */
     BLAZE_CONSTRAINT_MUST_BE_SPARSE_MATRIX_TYPE       ( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_REFERENCE_TYPE       ( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_POINTER_TYPE         ( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_CONST                ( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_VOLATILE             ( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_EXPRESSION_TYPE      ( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_SYMMETRIC_MATRIX_TYPE( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_HERMITIAN_MATRIX_TYPE( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_LOWER_MATRIX_TYPE    ( MT );
     BLAZE_CONSTRAINT_MUST_NOT_BE_UPPER_MATRIX_TYPE    ( MT );
     BLAZE_CONSTRAINT_MUST_BE_NUMERIC_TYPE             ( ElementType );
     /*! \endcond */
     //**********************************************************************************************
  };
  //*************************************************************************************************
  
  
  
  
  //=================================================================================================
  //
  //  CONSTRUCTORS
  //
  //=================================================================================================
  
  //*************************************************************************************************
  /*!\brief Constructor for the UniLowerElement class.
  //
  // \param pos Iterator to the current position with the sparse lower unitriangular matrix.
  // \param diagonal \a true in case the element is on the diagonal, \a false if not.
  */
  template< typename MT >  // Type of the adapted matrix
  inline UniLowerElement<MT>::UniLowerElement( IteratorType pos, bool diagonal )
     : pos_     ( pos      )  // Iterator to the current lower unitriangular matrix element
     , diagonal_( diagonal )  // true in case the element is on the diagonal, false if not
  {}
  //*************************************************************************************************
  
  
  
  
  //=================================================================================================
  //
  //  OPERATORS
  //
  //=================================================================================================
  
  //*************************************************************************************************
  /*!\brief Assignment to the unilower element.
  //
  // \param v The new value of the unilower element.
  // \return Reference to the assigned unilower element.
  // \exception std::invalid_argument Invalid assignment to diagonal matrix element.
  */
  template< typename MT >  // Type of the adapted matrix
  template< typename T >   // Type of the right-hand side value
  inline UniLowerElement<MT>& UniLowerElement<MT>::operator=( const T& v )
  {
     if( diagonal_ ) {
        BLAZE_THROW_INVALID_ARGUMENT( "Invalid assignment to diagonal matrix element" );
     }
  
     *pos_ = v;
  
     return *this;
  }
  //*************************************************************************************************
  
  
  //*************************************************************************************************
  /*!\brief Addition assignment to the unilower element.
  //
  // \param v The right-hand side value for the addition.
  // \return Reference to the assigned unilower element.
  // \exception std::invalid_argument Invalid assignment to diagonal matrix element.
  */
  template< typename MT >  // Type of the adapted matrix
  template< typename T >   // Type of the right-hand side value
  inline UniLowerElement<MT>& UniLowerElement<MT>::operator+=( const T& v )
  {
     if( diagonal_ ) {
        BLAZE_THROW_INVALID_ARGUMENT( "Invalid assignment to diagonal matrix element" );
     }
  
     *pos_ += v;
  
     return *this;
  }
  //*************************************************************************************************
  
  
  //*************************************************************************************************
  /*!\brief Subtraction assignment to the unilower element.
  //
  // \param v The right-hand side value for the subtraction.
  // \return Reference to the assigned unilower element.
  // \exception std::invalid_argument Invalid assignment to diagonal matrix element.
  */
  template< typename MT >  // Type of the adapted matrix
  template< typename T >   // Type of the right-hand side value
  inline UniLowerElement<MT>& UniLowerElement<MT>::operator-=( const T& v )
  {
     if( diagonal_ ) {
        BLAZE_THROW_INVALID_ARGUMENT( "Invalid assignment to diagonal matrix element" );
     }
  
     *pos_ -= v;
  
     return *this;
  }
  //*************************************************************************************************
  
  
  //*************************************************************************************************
  /*!\brief Multiplication assignment to the unilower element.
  //
  // \param v The right-hand side value for the multiplication.
  // \return Reference to the assigned unilower element.
  // \exception std::invalid_argument Invalid assignment to diagonal matrix element.
  */
  template< typename MT >  // Type of the adapted matrix
  template< typename T >   // Type of the right-hand side value
  inline UniLowerElement<MT>& UniLowerElement<MT>::operator*=( const T& v )
  {
     if( diagonal_ ) {
        BLAZE_THROW_INVALID_ARGUMENT( "Invalid assignment to diagonal matrix element" );
     }
  
     *pos_ *= v;
  
     return *this;
  }
  //*************************************************************************************************
  
  
  //*************************************************************************************************
  /*!\brief Division assignment to the unilower element.
  //
  // \param v The right-hand side value for the division.
  // \return Reference to the assigned unilower element.
  // \exception std::invalid_argument Invalid assignment to diagonal matrix element.
  */
  template< typename MT >  // Type of the adapted matrix
  template< typename T >   // Type of the right-hand side value
  inline UniLowerElement<MT>& UniLowerElement<MT>::operator/=( const T& v )
  {
     if( diagonal_ ) {
        BLAZE_THROW_INVALID_ARGUMENT( "Invalid assignment to diagonal matrix element" );
     }
  
     *pos_ /= v;
  
     return *this;
  }
  //*************************************************************************************************
  
  
  
  
  //=================================================================================================
  //
  //  ACCESS OPERATORS
  //
  //=================================================================================================
  
  //*************************************************************************************************
  /*!\brief Direct access to the unilower element.
  //
  // \return Reference to the value of the unilower element.
  */
  template< typename MT >  // Type of the adapted matrix
  inline typename UniLowerElement<MT>::Pointer UniLowerElement<MT>::operator->() noexcept
  {
     return this;
  }
  //*************************************************************************************************
  
  
  
  
  //=================================================================================================
  //
  //  UTILITY FUNCTIONS
  //
  //=================================================================================================
  
  //*************************************************************************************************
  /*!\brief Access to the current value of the unilower element.
  //
  // \return The current value of the unilower element.
  */
  template< typename MT >  // Type of the adapted matrix
  inline typename UniLowerElement<MT>::Reference UniLowerElement<MT>::value() const
  {
     return Reference( pos_->value(), diagonal_ );
  }
  //*************************************************************************************************
  
  
  //*************************************************************************************************
  /*!\brief Access to the current index of the unilower element.
  //
  // \return The current index of the unilower element.
  */
  template< typename MT >  // Type of the adapted matrix
  inline typename UniLowerElement<MT>::IndexType UniLowerElement<MT>::index() const
  {
     return pos_->index();
  }
  //*************************************************************************************************
  
  } // namespace blaze
  
  #endif
  