/***************************************************************************
                          DenseMatrixView.h  -  description
                             -------------------
    begin                : Nov 29, 2013
    copyright            : (C) 2013 by Tomas Oberhuber
    email                : tomas.oberhuber@fjfi.cvut.cz
 ***************************************************************************/

/* See Copyright Notice in tnl/Copyright */

#pragma once

#include <TNL/Allocators/Default.h>
#include <TNL/Devices/Host.h>
#include <TNL/Matrices/DenseMatrixRowView.h>
#include <TNL/Matrices/MatrixView.h>
#include <TNL/Matrices/MatrixType.h>
#include <TNL/Algorithms/Segments/Ellpack.h>

namespace TNL {
namespace Matrices {

/**
 * \brief Implementation of dense matrix view.
 *
 * It serves as an accessor to \ref DenseMatrix for example when passing the
 * matrix to lambda functions. DenseMatrix view can be also created in CUDA kernels.
 *
 * \tparam Real is a type of matrix elements.
 * \tparam Device is a device where the matrix is allocated.
 * \tparam Index is a type for indexing of the matrix elements.
 * \tparam MatrixElementsOrganization tells the ordering of matrix elements in memory. It is either
 *         \ref TNL::Algorithms::Segments::RowMajorOrder
 *         or \ref TNL::Algorithms::Segments::ColumnMajorOrder.
 *
 * See \ref DenseMatrix.
 */
template< typename Real = double,
          typename Device = Devices::Host,
          typename Index = int,
          ElementsOrganization Organization = Algorithms::Segments::DefaultElementsOrganization< Device >::getOrganization() >
class DenseMatrixView : public MatrixView< Real, Device, Index >
{
   protected:
      using BaseType = Matrix< Real, Device, Index >;
      using ValuesType = typename BaseType::ValuesType;
      using SegmentsType = Algorithms::Segments::Ellpack< Device, Index, typename Allocators::Default< Device >::template Allocator< Index >, Organization, 1 >;
      using SegmentsViewType = typename SegmentsType::ViewType;
      using SegmentViewType = typename SegmentsType::SegmentViewType;

   public:

      /**
       * \brief The type of matrix elements.
       */
      using RealType = Real;

      /**
       * \brief The device where the matrix is allocated.
       */
      using DeviceType = Device;

      /**
       * \brief The type used for matrix elements indexing.
       */
      using IndexType = Index;

      /**
       * \brief Matrix elements organization getter.
       *
       * \return matrix elements organization - RowMajorOrder of ColumnMajorOrder.
       */
      static constexpr ElementsOrganization getOrganization() { return Organization; };

      /**
       * \brief Matrix elements container view type.
       *
       * Use this for embedding of the matrix elements values.
       */
      using ValuesViewType = typename ValuesType::ViewType;

      /**
       * \brief Matrix elements container view type.
       *
       * Use this for embedding of the matrix elements values.
       */
      using ConstValuesViewType = typename ValuesType::ConstViewType;

      /**
       * \brief Matrix view type.
       *
       * See \ref DenseMatrixView.
       */
      using ViewType = DenseMatrixView< Real, Device, Index, Organization >;

      /**
       * \brief Matrix view type for constant instances.
       *
       * See \ref DenseMatrixView.
       */
      using ConstViewType = DenseMatrixView< std::add_const_t< Real >, Device, Index, Organization >;

      /**
       * \brief Type for accessing matrix row.
       */
      using RowView = DenseMatrixRowView< SegmentViewType, ValuesViewType >;

      /**
       * \brief Helper type for getting self type or its modifications.
       */
      template< typename _Real = Real,
                typename _Device = Device,
                typename _Index = Index >
      using Self = DenseMatrixView< _Real, _Device, _Index >;

      /**
       * \brief Constructor without parameters.
       */
      __cuda_callable__
      DenseMatrixView();

      /**
       * \brief Constructor with matrix dimensions and values.
       *
       * Organization of matrix elements values in
       *
       * \param rows number of matrix rows.
       * \param columns number of matrix columns.
       * \param values is vector view with matrix elements values.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_constructor.cpp
       * \par Output
       * \include DenseMatrixViewExample_constructor.out
       */
      __cuda_callable__
      DenseMatrixView( const IndexType rows,
                       const IndexType columns,
                       const ValuesViewType& values );

      /**
       * \brief Constructor with matrix dimensions and values.
       *
       * Organization of matrix elements values in
       *
       * \param rows number of matrix rows.
       * \param columns number of matrix columns.
       * \param values is vector view with matrix elements values.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_constructor.cpp
       * \par Output
       * \include DenseMatrixViewExample_constructor.out
       */
       template< typename Real_ >
      __cuda_callable__
      DenseMatrixView( const IndexType rows,
                       const IndexType columns,
                       const Containers::VectorView< Real_, Device, Index >& values );


      /**
       * \brief Copy constructor.
       *
       * \param matrix is the source matrix view.
       */
      __cuda_callable__
      DenseMatrixView( const DenseMatrixView& matrix ) = default;

      /**
       * \brief Returns a modifiable dense matrix view.
       *
       * \return dense matrix view.
       */
      __cuda_callable__
      ViewType getView();

      /**
       * \brief Returns a non-modifiable dense matrix view.
       *
       * \return dense matrix view.
       */
      __cuda_callable__
      ConstViewType getConstView() const;

      /**
       * \brief Returns string with serialization type.
       *
       * The string has a form \e `Matrices::DenseMatrix< RealType,  [any_device], IndexType, [any_allocator], true/false >`.
       *
       * \return \e String with the serialization type.
       */
      static String getSerializationType();

      /**
       * \brief Returns string with serialization type.
       *
       * See \ref DenseMatrixView::getSerializationType.
       *
       * \return \e String with the serialization type.
       */
      virtual String getSerializationTypeVirtual() const;

      /**
       * \brief Compute capacities of all rows.
       *
       * The row capacities are not stored explicitly and must be computed.
       *
       * \param rowCapacities is a vector where the row capacities will be stored.
       */
      template< typename Vector >
      void getRowCapacities( Vector& rowCapacities ) const;

      /**
       * \brief Computes number of non-zeros in each row.
       *
       * \param rowLengths is a vector into which the number of non-zeros in each row
       * will be stored.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_getCompressedRowLengths.cpp
       * \par Output
       * \include DenseMatrixViewExample_getCompressedRowLengths.out
       */
      template< typename Vector >
      void getCompressedRowLengths( Vector& rowLengths ) const;

      /**
       * \brief Returns number of all matrix elements.
       *
       * This method is here mainly for compatibility with sparse matrices since
       * the number of all matrix elements is just number of rows times number of
       * columns.
       *
       * \return number of all matrix elements.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_getElementsCount.cpp
       * \par Output
       * \include DenseMatrixViewExample_getElementsCount.out
       */
      IndexType getAllocatedElementsCount() const;

      /**
       * \brief Returns number of non-zero matrix elements.
       *
       * \return number of all non-zero matrix elements.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_getElementsCount.cpp
       * \par Output
       * \include DenseMatrixViewExample_getElementsCount.out
       */
      IndexType getNonzeroElementsCount() const;

      /**
       * \brief Constant getter of simple structure for accessing given matrix row.
       *
       * \param rowIdx is matrix row index.
       *
       * \return RowView for accessing given matrix row.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_getConstRow.cpp
       * \par Output
       * \include DenseMatrixViewExample_getConstRow.out
       *
       * See \ref DenseMatrixRowView.
       */
      __cuda_callable__
      const RowView getRow( const IndexType& rowIdx ) const;

      /**
       * \brief Non-constant getter of simple structure for accessing given matrix row.
       *
       * \param rowIdx is matrix row index.
       *
       * \return RowView for accessing given matrix row.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_getRow.cpp
       * \par Output
       * \include DenseMatrixExample_getRow.out
       *
       * See \ref DenseMatrixRowView.
       */
      __cuda_callable__
      RowView getRow( const IndexType& rowIdx );

      /**
       * \brief Sets all matrix elements to value \e v.
       *
       * \param v is value all matrix elements will be set to.
       */
      void setValue( const RealType& v );

      /**
       * \brief Returns non-constant reference to element at row \e row and column column.
       *
       * Since this method returns reference to the element, it cannot be called across
       * different address spaces. It means that it can be called only form CPU if the matrix
       * is allocated on CPU or only from GPU kernels if the matrix is allocated on GPU.
       *
       * \param row is a row index of the element.
       * \param column is a columns index of the element.
       * \return reference to given matrix element.
       */
      __cuda_callable__
      Real& operator()( const IndexType row,
                        const IndexType column );

      /**
       * \brief Returns constant reference to element at row \e row and column column.
       *
       * Since this method returns reference to the element, it cannot be called across
       * different address spaces. It means that it can be called only form CPU if the matrix
       * is allocated on CPU or only from GPU kernels if the matrix is allocated on GPU.
       *
       * \param row is a row index of the element.
       * \param column is a columns index of the element.
       * \return reference to given matrix element.
       */
      __cuda_callable__
      const Real& operator()( const IndexType row,
                              const IndexType column ) const;

      /**
       * \brief Sets element at given \e row and \e column to given \e value.
       *
       * This method can be called from the host system (CPU) no matter
       * where the matrix is allocated. If the matrix is allocated on GPU this method
       * can be called even from device kernels. If the matrix is allocated in GPU device
       * this method is called from CPU, it transfers values of each matrix element separately and so the
       * performance is very low. For higher performance see. \ref DenseMatrix::getRow
       * or \ref DenseMatrix::forElements and \ref DenseMatrix::forAllElements.
       *
       * \param row is row index of the element.
       * \param column is columns index of the element.
       * \param value is the value the element will be set to.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_setElement.cpp
       * \par Output
       * \include DenseMatrixExample_setElement.out
       */
      __cuda_callable__
      void setElement( const IndexType row,
                       const IndexType column,
                       const RealType& value );

      /**
       * \brief Add element at given \e row and \e column to given \e value.
       *
       * This method can be called from the host system (CPU) no matter
       * where the matrix is allocated. If the matrix is allocated on GPU this method
       * can be called even from device kernels. If the matrix is allocated in GPU device
       * this method is called from CPU, it transfers values of each matrix element separately and so the
       * performance is very low. For higher performance see. \ref DenseMatrix::getRow
       * or \ref DenseMatrix::forElements and \ref DenseMatrix::forAllElements.
       *
       * \param row is row index of the element.
       * \param column is columns index of the element.
       * \param value is the value the element will be set to.
       * \param thisElementMultiplicator is multiplicator the original matrix element
       *   value is multiplied by before addition of given \e value.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_addElement.cpp
       * \par Output
       * \include DenseMatrixExample_addElement.out
       *
       */
      __cuda_callable__
      void addElement( const IndexType row,
                       const IndexType column,
                       const RealType& value,
                       const RealType& thisElementMultiplicator = 1.0 );

      /**
       * \brief Returns value of matrix element at position given by its row and column index.
       *
       * This method can be called from the host system (CPU) no matter
       * where the matrix is allocated. If the matrix is allocated on GPU this method
       * can be called even from device kernels. If the matrix is allocated in GPU device
       * this method is called from CPU, it transfers values of each matrix element separately and so the
       * performance is very low. For higher performance see. \ref DenseMatrix::getRow
       * or \ref DenseMatrix::forElements and \ref DenseMatrix::forAllElements.
       *
       * \param row is a row index of the matrix element.
       * \param column i a column index of the matrix element.
       *
       * \return value of given matrix element.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_getElement.cpp
       * \par Output
       * \include DenseMatrixExample_getElement.out
       *
       */
      __cuda_callable__
      Real getElement( const IndexType row,
                       const IndexType column ) const;

      /**
       * \brief Method for performing general reduction on matrix rows.
       *
       * \tparam Fetch is a type of lambda function for data fetch declared as
       *          `fetch( IndexType rowIdx, IndexType columnIdx, RealType elementValue ) -> FetchValue`.
       *          The return type of this lambda can be any non void.
       * \tparam Reduce is a type of lambda function for reduction declared as
       *          `reduce( const FetchValue& v1, const FetchValue& v2 ) -> FetchValue`.
       * \tparam Keep is a type of lambda function for storing results of reduction in each row.
       *          It is declared as `keep( const IndexType rowIdx, const double& value )`.
       * \tparam FetchValue is type returned by the Fetch lambda function.
       *
       * \param begin defines beginning of the range [begin,end) of rows to be processed.
       * \param end defines ending of the range [begin,end) of rows to be processed.
       * \param fetch is an instance of lambda function for data fetch.
       * \param reduce is an instance of lambda function for reduction.
       * \param keep in an instance of lambda function for storing results.
       * \param identity is the [identity element](https://en.wikipedia.org/wiki/Identity_element)
       *                 for the reduction operation, i.e. element which does not
       *                 change the result of the reduction.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_reduceRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_reduceRows.out
       */
      template< typename Fetch, typename Reduce, typename Keep, typename FetchReal >
      void reduceRows( IndexType begin, IndexType end, Fetch& fetch, const Reduce& reduce, Keep& keep, const FetchReal& identity );

      /**
       * \brief Method for performing general reduction on matrix rows for constant instances.
       *
       * \tparam Fetch is a type of lambda function for data fetch declared as
       *          `fetch( IndexType rowIdx, IndexType columnIdx, RealType elementValue ) -> FetchValue`.
       *          The return type of this lambda can be any non void.
       * \tparam Reduce is a type of lambda function for reduction declared as
       *          `reduce( const FetchValue& v1, const FetchValue& v2 ) -> FetchValue`.
       * \tparam Keep is a type of lambda function for storing results of reduction in each row.
       *          It is declared as `keep( const IndexType rowIdx, const double& value )`.
       * \tparam FetchValue is type returned by the Fetch lambda function.
       *
       * \param begin defines beginning of the range [begin,end) of rows to be processed.
       * \param end defines ending of the range [begin,end) of rows to be processed.
       * \param fetch is an instance of lambda function for data fetch.
       * \param reduce is an instance of lambda function for reduction.
       * \param keep in an instance of lambda function for storing results.
       * \param identity is the [identity element](https://en.wikipedia.org/wiki/Identity_element)
       *                 for the reduction operation, i.e. element which does not
       *                 change the result of the reduction.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_reduceRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_reduceRows.out
       */
      template< typename Fetch, typename Reduce, typename Keep, typename FetchReal >
      void reduceRows( IndexType begin, IndexType end, Fetch& fetch, const Reduce& reduce, Keep& keep, const FetchReal& identity ) const;

      /**
       * \brief Method for performing general reduction on ALL matrix rows.
       *
       * \tparam Fetch is a type of lambda function for data fetch declared as
       *          `fetch( IndexType rowIdx, IndexType columnIdx, RealType elementValue ) -> FetchValue`.
       *          The return type of this lambda can be any non void.
       * \tparam Reduce is a type of lambda function for reduction declared as
       *          `reduce( const FetchValue& v1, const FetchValue& v2 ) -> FetchValue`.
       * \tparam Keep is a type of lambda function for storing results of reduction in each row.
       *          It is declared as `keep( const IndexType rowIdx, const double& value )`.
       * \tparam FetchValue is type returned by the Fetch lambda function.
       *
       * \param fetch is an instance of lambda function for data fetch.
       * \param reduce is an instance of lambda function for reduction.
       * \param keep in an instance of lambda function for storing results.
       * \param identity is the [identity element](https://en.wikipedia.org/wiki/Identity_element)
       *                 for the reduction operation, i.e. element which does not
       *                 change the result of the reduction.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_reduceAllRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_reduceAllRows.out
       */
      template< typename Fetch, typename Reduce, typename Keep, typename FetchReal >
      void reduceAllRows( Fetch& fetch, const Reduce& reduce, Keep& keep, const FetchReal& identity );

      /**
       * \brief Method for performing general reduction on ALL matrix rows for constant instances.
       *
       * \tparam Fetch is a type of lambda function for data fetch declared as
       *          `fetch( IndexType rowIdx, IndexType columnIdx, RealType elementValue ) -> FetchValue`.
       *          The return type of this lambda can be any non void.
       * \tparam Reduce is a type of lambda function for reduction declared as
       *          `reduce( const FetchValue& v1, const FetchValue& v2 ) -> FetchValue`.
       * \tparam Keep is a type of lambda function for storing results of reduction in each row.
       *          It is declared as `keep( const IndexType rowIdx, const double& value )`.
       * \tparam FetchValue is type returned by the Fetch lambda function.
       *
       * \param fetch is an instance of lambda function for data fetch.
       * \param reduce is an instance of lambda function for reduction.
       * \param keep in an instance of lambda function for storing results.
       * \param identity is the [identity element](https://en.wikipedia.org/wiki/Identity_element)
       *                 for the reduction operation, i.e. element which does not
       *                 change the result of the reduction.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_reduceAllRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_reduceAllRows.out
       */
      template< typename Fetch, typename Reduce, typename Keep, typename FetchReal >
      void reduceAllRows( Fetch& fetch, const Reduce& reduce, Keep& keep, const FetchReal& identity ) const;

      /**
       * \brief Method for iteration over all matrix rows for constant instances.
       *
       * \tparam Function is type of lambda function that will operate on matrix elements.
       *    It is should have form like
       *  `function( IndexType rowIdx, IndexType columnIdx, IndexType columnIdx, const RealType& value, bool& compute )`.
       *  The column index repeats twice only for compatibility with sparse matrices.
       *  If the 'compute' variable is set to false the iteration over the row can
       *  be interrupted.
       *
       * \param begin defines beginning of the range [begin,end) of rows to be processed.
       * \param end defines ending of the range [begin,end) of rows to be processed.
       * \param function is an instance of the lambda function to be called in each row.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_forRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_forRows.out
       */
      template< typename Function >
      void forElements( IndexType begin, IndexType end, Function&& function ) const;

      /**
       * \brief Method for iteration over all matrix rows for non-constant instances.
       *
       * \tparam Function is type of lambda function that will operate on matrix elements.
       *    It is should have form like
       *  `function( IndexType rowIdx, IndexType columnIdx, IndexType columnIdx, RealType& value, bool& compute )`.
       *  The column index repeats twice only for compatibility with sparse matrices.
       *  If the 'compute' variable is set to false the iteration over the row can
       *  be interrupted.
       *
       * \param begin defines beginning of the range [begin,end) of rows to be processed.
       * \param end defines ending of the range [begin,end) of rows to be processed.
       * \param function is an instance of the lambda function to be called in each row.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_forRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_forRows.out
       */
      template< typename Function >
      void forElements( IndexType begin, IndexType end, Function&& function );

      /**
       * \brief This method calls \e forElements for all matrix rows.
       *
       * See \ref DenseMatrix::forElements.
       *
       * \tparam Function is a type of lambda function that will operate on matrix elements.
       * \param function  is an instance of the lambda function to be called in each row.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_forAllRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_forAllRows.out
       */
      template< typename Function >
      void forAllElements( Function&& function ) const;

      /**
       * \brief This method calls \e forElements for all matrix rows.
       *
       * See \ref DenseMatrix::forAllElements.
       *
       * \tparam Function is a type of lambda function that will operate on matrix elements.
       * \param function  is an instance of the lambda function to be called in each row.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixExample_forAllRows.cpp
       * \par Output
       * \include DenseMatrixExample_forAllRows.out
       */
      template< typename Function >
      void forAllElements( Function&& function );

      /**
       * \brief Method for parallel iteration over matrix rows from interval [ \e begin, \e end).
       *
       * In each row, given lambda function is performed. Each row is processed by at most one thread unlike the method
       * \ref DenseMatrix::forElements where more than one thread can be mapped to each row.
       *
       * \tparam Function is type of the lambda function.
       *
       * \param begin defines beginning of the range [ \e begin,\e end ) of rows to be processed.
       * \param end defines ending of the range [ \e begin, \e end ) of rows to be processed.
       * \param function is an instance of the lambda function to be called for each row.
       *
       * ```
       * auto function = [] __cuda_callable__ ( RowViewType& row ) mutable { ... };
       * ```
       *
       * \e RowViewType represents matrix row - see \ref TNL::Matrices::DenseMatrix::RowViewType.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixExample_forRows.cpp
       * \par Output
       * \include DenseMatrixExample_forRows.out
       */
      template< typename Function >
      void forRows( IndexType begin, IndexType end, Function&& function );

      /**
       * \brief Method for parallel iteration over matrix rows from interval [ \e begin, \e end) for constant instances.
       *
       * In each row, given lambda function is performed. Each row is processed by at most one thread unlike the method
       * \ref DenseMatrixView::forElements where more than one thread can be mapped to each row.
       *
       * \tparam Function is type of the lambda function.
       *
       * \param begin defines beginning of the range [ \e begin,\e end ) of rows to be processed.
       * \param end defines ending of the range [ \e begin, \e end ) of rows to be processed.
       * \param function is an instance of the lambda function to be called for each row.
       *
       * ```
       * auto function = [] __cuda_callable__ ( RowViewType& row ) { ... };
       * ```
       *
       * \e RowViewType represents matrix row - see \ref TNL::Matrices::DenseMatrixView::RowViewType.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_forRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_forRows.out
       */
      template< typename Function >
      void forRows( IndexType begin, IndexType end, Function&& function ) const;

      /**
       * \brief Method for parallel iteration over all matrix rows.
       *
       * In each row, given lambda function is performed. Each row is processed by at most one thread unlike the method
       * \ref DenseMatrixView::forAllElements where more than one thread can be mapped to each row.
       *
       * \tparam Function is type of the lambda function.
       *
       * \param function is an instance of the lambda function to be called for each row.
       *
       * ```
       * auto function = [] __cuda_callable__ ( RowViewType& row ) mutable { ... };
       * ```
       *
       * \e RowViewType represents matrix row - see \ref TNL::Matrices::DenseMatrixView::RowViewType.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_forRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_forRows.out
       */
      template< typename Function >
      void forAllRows( Function&& function );

      /**
       * \brief Method for parallel iteration over all matrix rows for constant instances.
       *
       * In each row, given lambda function is performed. Each row is processed by at most one thread unlike the method
       * \ref DenseMatrixView::forAllElements where more than one thread can be mapped to each row.
       *
       * \tparam Function is type of the lambda function.
       *
       * \param function is an instance of the lambda function to be called for each row.
       *
       * ```
       * auto function = [] __cuda_callable__ ( RowViewType& row ) { ... };
       * ```
       *
       * \e RowViewType represents matrix row - see \ref TNL::Matrices::DenseMatrixView::RowViewType.
       *
       * \par Example
       * \include Matrices/DenseMatrix/DenseMatrixViewExample_forRows.cpp
       * \par Output
       * \include DenseMatrixViewExample_forRows.out
       */
      template< typename Function >
      void forAllRows( Function&& function ) const;

      /**
       * \brief Method for sequential iteration over all matrix rows for constant instances.
       *
       * \tparam Function is type of lambda function that will operate on matrix elements.
       *    It is should have form like
       *  `function( IndexType rowIdx, IndexType columnIdx, IndexType columnIdx_, const RealType& value, bool& compute )`.
       *  The column index repeats twice only for compatibility with sparse matrices.
       *  If the 'compute' variable is set to false the iteration over the row can
       *  be interrupted.
       *
       * \param begin defines beginning of the range [begin,end) of rows to be processed.
       * \param end defines ending of the range [begin,end) of rows to be processed.
       * \param function is an instance of the lambda function to be called in each row.
       */
      template< typename Function >
      void sequentialForRows( IndexType begin, IndexType end, Function&& function ) const;

      /**
       * \brief Method for sequential iteration over all matrix rows for non-constant instances.
       *
       * \tparam Function is type of lambda function that will operate on matrix elements.
       *    It is should have form like
       *  `function( IndexType rowIdx, IndexType columnIdx, IndexType columnIdx_, RealType& value, bool& compute )`.
       *  The column index repeats twice only for compatibility with sparse matrices.
       *  If the 'compute' variable is set to false the iteration over the row can
       *  be interrupted.
       *
       * \param begin defines beginning of the range [begin,end) of rows to be processed.
       * \param end defines ending of the range [begin,end) of rows to be processed.
       * \param function is an instance of the lambda function to be called in each row.
       */
      template< typename Function >
      void sequentialForRows( IndexType begin, IndexType end, Function&& function );

      /**
       * \brief This method calls \e sequentialForRows for all matrix rows (for constant instances).
       *
       * See \ref DenseMatrixView::sequentialForRows.
       *
       * \tparam Function is a type of lambda function that will operate on matrix elements.
       * \param function  is an instance of the lambda function to be called in each row.
       */
      template< typename Function >
      void sequentialForAllRows( Function&& function ) const;

      /**
       * \brief This method calls \e sequentialForRows for all matrix rows.
       *
       * See \ref DenseMatrixView::sequentialForAllRows.
       *
       * \tparam Function is a type of lambda function that will operate on matrix elements.
       * \param function  is an instance of the lambda function to be called in each row.
       */
      template< typename Function >
      void sequentialForAllRows( Function&& function );

      /**
       * \brief Computes product of matrix and vector.
       *
       * More precisely, it computes:
       *
       * `outVector = matrixMultiplicator * ( *this ) * inVector + outVectorMultiplicator * outVector`
       *
       * \tparam InVector is type of input vector.  It can be \ref Vector,
       *     \ref VectorView, \ref Array, \ref ArraView or similar container.
       * \tparam OutVector is type of output vector. It can be \ref Vector,
       *     \ref VectorView, \ref Array, \ref ArraView or similar container.
       *
       * \param inVector is input vector.
       * \param outVector is output vector.
       * \param matrixMultiplicator is a factor by which the matrix is multiplied. It is one by default.
       * \param outVectorMultiplicator is a factor by which the outVector is multiplied before added
       *    to the result of matrix-vector product. It is zero by default.
       * \param begin is the beginning of the rows range for which the vector product
       *    is computed. It is zero by default.
       * \param end is the end of the rows range for which the vector product
       *    is computed. It is number if the matrix rows by default.
       *
       * Note that the ouput vector dimension must be the same as the number of matrix rows
       * no matter how we set `begin` and `end` parameters. These parameters just say that
       * some matrix rows and the output vector elements are omitted.
       */
      template< typename InVector, typename OutVector >
      void vectorProduct( const InVector& inVector,
                          OutVector& outVector,
                          const RealType& matrixMultiplicator = 1.0,
                          const RealType& outVectorMultiplicator = 0.0,
                          const IndexType begin = 0,
                          IndexType end = 0 ) const;

      template< typename Matrix >
      void addMatrix( const Matrix& matrix,
                      const RealType& matrixMultiplicator = 1.0,
                      const RealType& thisMatrixMultiplicator = 1.0 );

      template< typename Matrix1, typename Matrix2, int tileDim = 32 >
      void getMatrixProduct( const Matrix1& matrix1,
                          const Matrix2& matrix2,
                          const RealType& matrix1Multiplicator = 1.0,
                          const RealType& matrix2Multiplicator = 1.0 );

      template< typename Matrix, int tileDim = 32 >
      void getTransposition( const Matrix& matrix,
                             const RealType& matrixMultiplicator = 1.0 );

      template< typename Vector1, typename Vector2 >
      void performSORIteration( const Vector1& b,
                                const IndexType row,
                                Vector2& x,
                                const RealType& omega = 1.0 ) const;

      /**
       * \brief Assignment operator with DenseMatrix.
       *
       * \param matrix is the right-hand side matrix.
       * \return reference to this matrix.
       */
      DenseMatrixView& operator=( const DenseMatrixView& matrix );

      /**
       * \brief Method for saving the matrix view to the file with given filename.
       *
       * The ouput file can be loaded by \ref DenseMatrix.
       *
       * \param fileName is name of the file.
       */
      void save( const String& fileName ) const;

      /**
       * \brief Method for saving the matrix view to a file.
       *
       * The ouput file can be loaded by \ref DenseMatrix.
       *
       * \param fileName is name of the file.
       */
      void save( File& file ) const;

      /**
       * \brief Method for printing the matrix to output stream.
       *
       * \param str is the output stream.
       */
      void print( std::ostream& str ) const;

   protected:

      __cuda_callable__
      IndexType getElementIndex( const IndexType row,
                                 const IndexType column ) const;

      SegmentsViewType segments;
};

} // namespace Matrices
} // namespace TNL

#include <TNL/Matrices/DenseMatrixView.hpp>
