/***************************************************************************
                          LaxFridrichsEnergy.h  -  description
                             -------------------
    begin                : Feb 17, 2017
    copyright            : (C) 2017 by Tomas Oberhuber
    email                : tomas.oberhuber@fjfi.cvut.cz
 ***************************************************************************/

/* See Copyright Notice in tnl/Copyright */

#pragma once

#include <TNL/Containers/Vector.h>
#include <TNL/Meshes/Grid.h>

namespace TNL {
   
template< typename Mesh,
          typename Real = typename Mesh::RealType,
          typename Index = typename Mesh::IndexType >
class LaxFridrichsEnergyBase
{
   public:
      
      typedef Real RealType;
      typedef Index IndexType;
      typedef Mesh MeshType;
      typedef typename MeshType::DeviceType DeviceType;
      typedef typename MeshType::CoordinatesType CoordinatesType;
      typedef Functions::MeshFunction< MeshType > MeshFunctionType;
      static const int Dimensions = MeshType::getMeshDimension();
      typedef Functions::VectorField< Dimensions, MeshFunctionType > VelocityFieldType;
      typedef Pointers::SharedPointer< MeshFunctionType > MeshFunctionPointer;
      typedef Pointers::SharedPointer< VelocityFieldType > VelocityFieldPointer;
      
      LaxFridrichsEnergyBase()
       : artificialViscosity( 1.0 ){};

      static String getType()
      {
         return String( "LaxFridrichsEnergy< " ) +
             MeshType::getType() + ", " +
             TNL::getType< Real >() + ", " +
             TNL::getType< Index >() + " >"; 
      }

      void setTau(const Real& tau)
      {
          this->tau = tau;
      };
      
      void setVelocity( const VelocityFieldPointer& velocity )
      {
          this->velocity = velocity;
      };
      
      void setPressure( const MeshFunctionPointer& pressure )
      {
          this->pressure = pressure;
      };
      
      void setArtificialViscosity( const RealType& artificialViscosity )
      {
         this->artificialViscosity = artificialViscosity;
      }      
      
      void setDynamicalViscosity( const RealType& dynamicalViscosity )
      {
         this->dynamicalViscosity = dynamicalViscosity;
      }  

      protected:
         
         RealType tau;
         
         VelocityFieldPointer velocity;
         
         MeshFunctionPointer pressure;
         
         RealType artificialViscosity, dynamicalViscosity;
};
   
template< typename Mesh,
          typename Real = typename Mesh::RealType,
          typename Index = typename Mesh::IndexType >
class LaxFridrichsEnergy
{
};

template< typename MeshReal,
          typename Device,
          typename MeshIndex,
          typename Real,
          typename Index >
class LaxFridrichsEnergy< Meshes::Grid< 1, MeshReal, Device, MeshIndex >, Real, Index >
   : public LaxFridrichsEnergyBase< Meshes::Grid< 1, MeshReal, Device, MeshIndex >, Real, Index >
{
   public:

      typedef Meshes::Grid< 1, MeshReal, Device, MeshIndex > MeshType;
      typedef LaxFridrichsEnergyBase< MeshType, Real, Index > BaseType;
      
      using typename BaseType::RealType;
      using typename BaseType::IndexType;
      using typename BaseType::DeviceType;
      using typename BaseType::CoordinatesType;
      using typename BaseType::MeshFunctionType;
      using typename BaseType::MeshFunctionPointer;
      using typename BaseType::VelocityFieldType;
      using typename BaseType::VelocityFieldPointer;
      using BaseType::Dimensions;      
      
      template< typename MeshFunction, typename MeshEntity >
      __cuda_callable__
      Real operator()( const MeshFunction& e,
                       const MeshEntity& entity,
                       const RealType& time = 0.0 ) const
      {
         static_assert( MeshEntity::getEntityDimension() == 1, "Wrong mesh entity dimensions." ); 
         static_assert( MeshFunction::getEntitiesDimension() == 1, "Wrong preimage function" ); 
         const typename MeshEntity::template NeighborEntities< 1 >& neighborEntities = entity.getNeighborEntities(); 

         const RealType& hxInverse = entity.getMesh().template getSpaceStepsProducts< -1 >(); 
         const RealType& hxSquareInverse = entity.getMesh().template getSpaceStepsProducts< -2 >(); 

         const IndexType& center = entity.getIndex(); 
         const IndexType& east = neighborEntities.template getEntityIndex< 1 >(); 
         const IndexType& west = neighborEntities.template getEntityIndex< -1 >();

         const RealType& pressure_west = this->pressure.template getData< DeviceType >()[ west ];
         const RealType& pressure_east = this->pressure.template getData< DeviceType >()[ east ];

         const RealType& velocity_x_east = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ east ];
         const RealType& velocity_x_west = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ west ];
         const RealType& velocity_x_center = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ center ];

         return 1.0 / ( 2.0 * this->tau ) * this->artificialViscosity * ( e[ west ] - 2.0 * e[ center ]  + e[ east ] ) 
                - 0.5 * ( ( e[ east ] + pressure_east ) * velocity_x_east  
                         - ( e[ west ] + pressure_west ) * velocity_x_west ) * hxInverse
// 1D uT_11_x
                - 4.0 / 3.0 * ( velocity_x_east * velocity_x_center - velocity_x_center * velocity_x_west
                              - velocity_x_center * velocity_x_center + velocity_x_west * velocity_x_west
                              ) * hxSquareInverse / 4
                * this->dynamicalViscosity;
      }

      /*template< typename MeshEntity >
      __cuda_callable__
      Index getLinearSystemRowLength( const MeshType& mesh,
                                      const IndexType& index,
                                      const MeshEntity& entity ) const;

      template< typename MeshEntity, typename Vector, typename MatrixRow >
      __cuda_callable__
      void updateLinearSystem( const RealType& time,
                               const RealType& tau,
                               const MeshType& mesh,
                               const IndexType& index,
                               const MeshEntity& entity,
                               const MeshFunctionType& u,
                               Vector& b,
                               MatrixRow& matrixRow ) const;*/
};

template< typename MeshReal,
          typename Device,
          typename MeshIndex,
          typename Real,
          typename Index >
class LaxFridrichsEnergy< Meshes::Grid< 2, MeshReal, Device, MeshIndex >, Real, Index >
   : public LaxFridrichsEnergyBase< Meshes::Grid< 2, MeshReal, Device, MeshIndex >, Real, Index >
{
   public:
      typedef Meshes::Grid< 2, MeshReal, Device, MeshIndex > MeshType;
      typedef LaxFridrichsEnergyBase< MeshType, Real, Index > BaseType;
      
      using typename BaseType::RealType;
      using typename BaseType::IndexType;
      using typename BaseType::DeviceType;
      using typename BaseType::CoordinatesType;
      using typename BaseType::MeshFunctionType;
      using typename BaseType::MeshFunctionPointer;
      using typename BaseType::VelocityFieldType;
      using typename BaseType::VelocityFieldPointer;
      using BaseType::Dimensions;
      

      template< typename MeshFunction, typename MeshEntity >
      __cuda_callable__
      Real operator()( const MeshFunction& e,
                       const MeshEntity& entity,
                       const RealType& time = 0.0 ) const
      {
         static_assert( MeshEntity::getEntityDimension() == 2, "Wrong mesh entity dimensions." ); 
         static_assert( MeshFunction::getEntitiesDimension() == 2, "Wrong preimage function" ); 
         const typename MeshEntity::template NeighborEntities< 2 >& neighborEntities = entity.getNeighborEntities(); 
 
         const RealType& hxInverse = entity.getMesh().template getSpaceStepsProducts< -1, 0 >(); 
         const RealType& hyInverse = entity.getMesh().template getSpaceStepsProducts< 0, -1 >();
         const RealType& hxSquareInverse = entity.getMesh().template getSpaceStepsProducts< -2, 0 >(); 
         const RealType& hySquareInverse = entity.getMesh().template getSpaceStepsProducts< 0, -2 >();  

         const IndexType& center = entity.getIndex(); 
         const IndexType& east  = neighborEntities.template getEntityIndex<  1,  0 >(); 
         const IndexType& west  = neighborEntities.template getEntityIndex< -1,  0 >(); 
         const IndexType& north = neighborEntities.template getEntityIndex<  0,  1 >(); 
         const IndexType& south = neighborEntities.template getEntityIndex<  0, -1 >();
         const IndexType& southEast = neighborEntities.template getEntityIndex<  1, -1 >();
         const IndexType& southWest = neighborEntities.template getEntityIndex<  -1, -1 >();
         const IndexType& northEast = neighborEntities.template getEntityIndex<  1, 1 >();
         const IndexType& northWest = neighborEntities.template getEntityIndex<  -1, 1 >();

         const RealType& pressure_west = this->pressure.template getData< DeviceType >()[ west ];
         const RealType& pressure_east = this->pressure.template getData< DeviceType >()[ east ];
         const RealType& pressure_north = this->pressure.template getData< DeviceType >()[ north ];
         const RealType& pressure_south = this->pressure.template getData< DeviceType >()[ south ];

         const RealType& velocity_x_north = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ north ];
         const RealType& velocity_x_south = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ south ];
         const RealType& velocity_x_east = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ east ];
         const RealType& velocity_x_west = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ west ];
         const RealType& velocity_x_center = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ center ];
         const RealType& velocity_x_southEast = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ southEast ];
         const RealType& velocity_x_southWest = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ southWest ];
         const RealType& velocity_x_northEast = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ northEast ];
         const RealType& velocity_x_northWest = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ northWest ];         

         const RealType& velocity_y_north = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ north ];
         const RealType& velocity_y_south = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ south ];
         const RealType& velocity_y_east = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ east ];
         const RealType& velocity_y_west = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ west ];
         const RealType& velocity_y_center = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ center ];
         const RealType& velocity_y_southEast = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ southEast ];
         const RealType& velocity_y_southWest = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ southWest ];
         const RealType& velocity_y_northEast = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ northEast ];
         const RealType& velocity_y_northWest = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ northWest ];         
         
         return 1.0 / ( 4.0 * this->tau ) * this->artificialViscosity * ( e[ west ] + e[ east ] + e[ south ] + e[ north ] - 4.0 * e[ center ] ) 
                - 0.5 * ( ( ( ( e[ east ] + pressure_east ) * velocity_x_east )
                          -( ( e[ west ] + pressure_west ) * velocity_x_west ) ) * hxInverse
                        + ( ( ( e[ north ] + pressure_north ) * velocity_y_north )
                          -( ( e[ south ] + pressure_south ) * velocity_y_south ) ) * hyInverse )
// 2D uT_11_x
                + ( 4.0 / 3.0 * ( velocity_x_east * velocity_x_center - velocity_x_center * velocity_x_west
                                - velocity_x_center * velocity_x_center + velocity_x_west * velocity_x_west
                                ) * hxSquareInverse
                  - 2.0 / 3.0 * ( velocity_y_northEast * velocity_x_east - velocity_y_southEast * velocity_x_east
                                - velocity_y_northWest * velocity_x_west + velocity_y_southWest * velocity_x_west
                                ) * hxInverse * hyInverse  / 4
                  ) * this->dynamicalViscosity 
// vT_21_x
                + ( ( velocity_y_northEast * velocity_y_east - velocity_y_southEast * velocity_y_east
                    - velocity_y_northWest * velocity_y_west + velocity_y_southWest * velocity_y_west
                    ) * hxInverse * hyInverse / 4
                  + ( velocity_x_east * velocity_y_center - velocity_x_center * velocity_y_west
                    - velocity_x_center * velocity_y_center + velocity_x_west * velocity_y_west
                    ) * hxSquareInverse
                  ) * this->dynamicalViscosity
// uT_12_y
                + ( ( velocity_x_northEast * velocity_x_north - velocity_x_southEast * velocity_x_south 
                    - velocity_x_northWest * velocity_x_north + velocity_x_southWest * velocity_x_south 
                    ) * hxInverse * hyInverse  / 4
                  + ( velocity_y_north * velocity_x_center - velocity_y_center * velocity_x_south
                    - velocity_y_center * velocity_x_center + velocity_y_south * velocity_x_south
                    ) * hySquareInverse
                ) * this->dynamicalViscosity
// 2D vT_22_y
                + ( 4.0 / 3.0 * ( velocity_y_north * velocity_y_center - velocity_y_center * velocity_y_south
                                - velocity_y_center * velocity_y_center + velocity_y_south * velocity_y_south
                                ) * hySquareInverse
                  - 2.0 / 3.0 * ( velocity_x_northEast * velocity_y_north - velocity_x_southEast * velocity_y_east 
                                - velocity_x_northWest * velocity_y_north + velocity_x_southWest * velocity_y_west
                                ) * hxInverse * hyInverse / 4
                ) * this->dynamicalViscosity;
      }

      /*template< typename MeshEntity >
      __cuda_callable__
      Index getLinearSystemRowLength( const MeshType& mesh,
                                      const IndexType& index,
                                      const MeshEntity& entity ) const;

      template< typename MeshEntity, typename Vector, typename MatrixRow >
      __cuda_callable__
      void updateLinearSystem( const RealType& time,
                               const RealType& tau,
                               const MeshType& mesh,
                               const IndexType& index,
                               const MeshEntity& entity,
                               const MeshFunctionType& u,
                               Vector& b,
                               MatrixRow& matrixRow ) const;*/
};

template< typename MeshReal,
          typename Device,
          typename MeshIndex,
          typename Real,
          typename Index >
class LaxFridrichsEnergy< Meshes::Grid< 3, MeshReal, Device, MeshIndex >, Real, Index >
   : public LaxFridrichsEnergyBase< Meshes::Grid< 3, MeshReal, Device, MeshIndex >, Real, Index >
{
   public:
      typedef Meshes::Grid< 3, MeshReal, Device, MeshIndex > MeshType;
      typedef LaxFridrichsEnergyBase< MeshType, Real, Index > BaseType;
      
      using typename BaseType::RealType;
      using typename BaseType::IndexType;
      using typename BaseType::DeviceType;
      using typename BaseType::CoordinatesType;
      using typename BaseType::MeshFunctionType;
      using typename BaseType::MeshFunctionPointer;
      using typename BaseType::VelocityFieldType;
      using typename BaseType::VelocityFieldPointer;
      using BaseType::Dimensions;      

      template< typename MeshFunction, typename MeshEntity >
      __cuda_callable__
      Real operator()( const MeshFunction& e,
                       const MeshEntity& entity,
                       const RealType& time = 0.0 ) const
      {
         static_assert( MeshEntity::getEntityDimension() == 3, "Wrong mesh entity dimensions." ); 
         static_assert( MeshFunction::getEntitiesDimension() == 3, "Wrong preimage function" ); 
         const typename MeshEntity::template NeighborEntities< 3 >& neighborEntities = entity.getNeighborEntities(); 
 
         const RealType& hxInverse = entity.getMesh().template getSpaceStepsProducts< -1, 0,  0 >(); 
         const RealType& hyInverse = entity.getMesh().template getSpaceStepsProducts< 0, -1,  0 >(); 
         const RealType& hzInverse = entity.getMesh().template getSpaceStepsProducts< 0,  0, -1 >(); 
         const RealType& hxSquareInverse = entity.getMesh().template getSpaceStepsProducts< -2, 0,  0 >(); 
         const RealType& hySquareInverse = entity.getMesh().template getSpaceStepsProducts< 0, -2,  0 >(); 
         const RealType& hzSquareInverse = entity.getMesh().template getSpaceStepsProducts< 0,  0, -2 >(); 

         const IndexType& center = entity.getIndex(); 
         const IndexType& east  = neighborEntities.template getEntityIndex<  1,  0,  0 >(); 
         const IndexType& west  = neighborEntities.template getEntityIndex< -1,  0,  0 >(); 
         const IndexType& north = neighborEntities.template getEntityIndex<  0,  1,  0 >(); 
         const IndexType& south = neighborEntities.template getEntityIndex<  0, -1,  0 >();
         const IndexType& up    = neighborEntities.template getEntityIndex<  0,  0,  1 >(); 
         const IndexType& down  = neighborEntities.template getEntityIndex<  0,  0, -1 >();
         const IndexType& northWest = neighborEntities.template getEntityIndex<  -1,  1,  0 >(); 
         const IndexType& northEast = neighborEntities.template getEntityIndex<  1,  1,  0 >(); 
         const IndexType& southWest = neighborEntities.template getEntityIndex<  -1, -1,  0 >();
         const IndexType& southEast = neighborEntities.template getEntityIndex<  1, -1,  0 >();
         const IndexType& upWest    = neighborEntities.template getEntityIndex<  -1,  0,  1 >();
         const IndexType& upEast    = neighborEntities.template getEntityIndex<  1,  0,  1 >();
         const IndexType& upSouth    = neighborEntities.template getEntityIndex<  0,  -1,  1 >();
         const IndexType& upNorth    = neighborEntities.template getEntityIndex<  0,  1,  1 >();
         const IndexType& downWest  = neighborEntities.template getEntityIndex<  -1,  0, -1 >();
         const IndexType& downEast  = neighborEntities.template getEntityIndex<  1,  0, -1 >();
         const IndexType& downSouth  = neighborEntities.template getEntityIndex<  0,  -1, -1 >();
         const IndexType& downNorth  = neighborEntities.template getEntityIndex<  0,  1, -1 >();
         
         const RealType& pressure_west  = this->pressure.template getData< DeviceType >()[ west ];
         const RealType& pressure_east  = this->pressure.template getData< DeviceType >()[ east ];
         const RealType& pressure_north = this->pressure.template getData< DeviceType >()[ north ];
         const RealType& pressure_south = this->pressure.template getData< DeviceType >()[ south ];
         const RealType& pressure_up    = this->pressure.template getData< DeviceType >()[ up ];
         const RealType& pressure_down  = this->pressure.template getData< DeviceType >()[ down ];
         
         const RealType& velocity_x_north  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ north ];
         const RealType& velocity_x_south  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ south ];
         const RealType& velocity_x_east  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ east ];
         const RealType& velocity_x_west  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ west ];
         const RealType& velocity_x_up  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ up ];
         const RealType& velocity_x_down  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ down ];
         const RealType& velocity_x_center  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ center ];
         const RealType& velocity_x_northWest  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ northWest ];
         const RealType& velocity_x_northEast  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ northEast ];
         const RealType& velocity_x_southWest  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ southWest ];
         const RealType& velocity_x_southEast  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ southEast ];
         const RealType& velocity_x_upWest  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ upWest ];
         const RealType& velocity_x_downWest  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ downWest ];
         const RealType& velocity_x_upEast  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ upEast ];
         const RealType& velocity_x_downEast  = this->velocity.template getData< DeviceType >()[ 0 ].template getData< DeviceType >()[ downEast ];

         const RealType& velocity_y_north = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ north ];
         const RealType& velocity_y_south = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ south ];
         const RealType& velocity_y_east = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ east ];
         const RealType& velocity_y_west = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ west ];
         const RealType& velocity_y_up = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ up ];
         const RealType& velocity_y_down = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ down ];
         const RealType& velocity_y_center = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ center ];
         const RealType& velocity_y_northWest = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ northWest ];
         const RealType& velocity_y_northEast = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ northEast ];
         const RealType& velocity_y_southWest = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ southWest ];
         const RealType& velocity_y_southEast = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ southEast ];
         const RealType& velocity_y_upNorth = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ upNorth ];
         const RealType& velocity_y_upSouth = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ upSouth ];
         const RealType& velocity_y_downNorth = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ downNorth ];
         const RealType& velocity_y_downSouth = this->velocity.template getData< DeviceType >()[ 1 ].template getData< DeviceType >()[ downSouth ];

         const RealType& velocity_z_north    = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ north ];
         const RealType& velocity_z_south  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ south ]; 
         const RealType& velocity_z_east    = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ east ];
         const RealType& velocity_z_west  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ west ]; 
         const RealType& velocity_z_up    = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ up ];
         const RealType& velocity_z_down  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ down ]; 
         const RealType& velocity_z_center  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ center ]; 
         const RealType& velocity_z_upWest  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ upWest ]; 
         const RealType& velocity_z_upEast  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ upEast ]; 
         const RealType& velocity_z_upNorth  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ upNorth ]; 
         const RealType& velocity_z_upSouth  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ upSouth ]; 
         const RealType& velocity_z_downWest  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ downWest ]; 
         const RealType& velocity_z_downEast  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ downEast ]; 
         const RealType& velocity_z_downNorth  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ downNorth ]; 
         const RealType& velocity_z_downSouth  = this->velocity.template getData< DeviceType >()[ 2 ].template getData< DeviceType >()[ downSouth ];         
         
         return 1.0 / ( 6.0 * this->tau ) * this->artificialViscosity *
                 ( e[ west ] + e[ east ] + e[ south ] + e[ north ] + e[ up ] + e[ down ] - 6.0 * e[ center ] ) 
                - 0.5 * ( ( ( ( e[ east ] + pressure_east ) * velocity_x_east )
                           -( ( e[ west ] + pressure_west ) * velocity_x_west ) ) * hxInverse
                        + ( ( ( e[ north ] + pressure_north ) * velocity_y_north )
                           -( ( e[ south ] + pressure_south ) * velocity_y_south ) ) * hyInverse
                        + ( ( ( e[ up ] + pressure_up ) * velocity_z_up )
                           -( ( e[ down ] + pressure_down ) * velocity_z_down ) ) * hzInverse )
// 3D uT_11_x
                + ( 4.0 / 3.0 * ( velocity_x_east * velocity_x_center - velocity_x_center * velocity_x_west
                                - velocity_x_center * velocity_x_center + velocity_x_west * velocity_x_west 
                                ) * hxSquareInverse
                  - 2.0 / 3.0 * ( velocity_y_northEast * velocity_x_east - velocity_y_southEast * velocity_x_east
                                - velocity_y_northWest * velocity_x_west + velocity_y_southWest * velocity_x_west
                                ) * hxInverse * hyInverse / 4
                  - 2.0 / 3.0 * ( velocity_z_upEast * velocity_x_east - velocity_z_downEast * velocity_x_east
                                - velocity_z_upWest * velocity_x_west + velocity_z_downWest * velocity_x_west
                                ) * hxInverse * hzInverse / 4
                  ) * this->dynamicalViscosity
// vT_21_x
                + ( ( velocity_y_northEast * velocity_y_east - velocity_y_southEast * velocity_y_east
                    - velocity_y_northWest * velocity_y_west + velocity_y_southWest * velocity_y_west
                    ) * hxInverse * hyInverse / 4
                  + ( velocity_x_east * velocity_y_center - velocity_x_center * velocity_y_west
                    - velocity_x_center * velocity_y_center + velocity_x_west * velocity_y_west
                    ) * hxSquareInverse
                  ) * this->dynamicalViscosity
// wT_31_x
                + ( ( velocity_z_upEast * velocity_z_east - velocity_z_downEast * velocity_z_east
                    - velocity_z_upWest * velocity_z_west + velocity_z_downWest * velocity_z_west
                    ) * hxInverse * hzInverse / 4
                  + ( velocity_x_east * velocity_z_center - velocity_x_center * velocity_z_west 
                    - velocity_x_center * velocity_z_center + velocity_x_west * velocity_z_west
                    ) * hxSquareInverse
                  ) * this->dynamicalViscosity
// uT_12_y
                + ( ( velocity_x_northEast * velocity_x_north - velocity_x_southEast * velocity_x_south
                    - velocity_x_northWest * velocity_x_north + velocity_x_southWest * velocity_x_south
                    ) * hxInverse * hyInverse / 4
                  + ( velocity_y_north * velocity_x_center - velocity_y_center * velocity_x_south
                    + velocity_y_center * velocity_x_center + velocity_y_south * velocity_x_south
                    ) * hySquareInverse
                  ) * this->dynamicalViscosity
// 3D vT_22_y
                + ( 4.0 / 3.0 * ( velocity_y_north * velocity_y_center - velocity_y_center * velocity_y_south
                                - velocity_y_center * velocity_y_center + velocity_y_south * velocity_y_south
                                ) * hySquareInverse
                  - 2.0 / 3.0 * ( velocity_x_northEast * velocity_y_north - velocity_x_southEast * velocity_y_south
                                - velocity_x_northWest * velocity_y_north + velocity_x_southWest * velocity_y_south
                                ) * hxInverse * hyInverse / 4
                  - 2.0 / 3.0 * ( velocity_z_upNorth * velocity_y_north - velocity_z_downNorth * velocity_y_north
                                - velocity_z_upSouth * velocity_y_south + velocity_z_downSouth * velocity_y_south
                                ) * hyInverse * hzInverse / 4
                  ) * this->dynamicalViscosity
// wT_32_y
                + ( ( velocity_z_upNorth * velocity_z_north - velocity_z_downNorth * velocity_y_north
                    - velocity_z_upSouth * velocity_z_south + velocity_z_downSouth * velocity_z_south
                    ) * hyInverse * hzInverse / 4
                  + ( velocity_y_north * velocity_z_center - velocity_y_center * velocity_z_south
                    - velocity_y_center * velocity_z_center + velocity_y_south * velocity_z_south
                    ) * hySquareInverse
                  ) * this->dynamicalViscosity
// uT_13_z
                + ( ( velocity_z_up * velocity_x_center - velocity_z_center * velocity_x_center 
                    - velocity_z_center * velocity_x_down + velocity_z_down * velocity_x_down
                    ) * hzSquareInverse
                  + ( velocity_x_upEast * velocity_x_up - velocity_x_downEast * velocity_x_down
                    - velocity_x_upWest * velocity_x_up + velocity_x_downWest * velocity_x_down
                    ) * hxInverse * hzInverse / 4
                  ) * this->dynamicalViscosity
// T_23_z
                + ( ( velocity_y_upNorth * velocity_y_up - velocity_y_downNorth * velocity_y_down
                    - velocity_y_upSouth * velocity_y_up + velocity_y_downSouth * velocity_y_down
                    ) * hyInverse * hzInverse / 4
                  + ( velocity_z_up * velocity_y_center - velocity_z_center * velocity_y_down
                    - velocity_z_center * velocity_y_center + velocity_z_down * velocity_y_down
                    ) * hzSquareInverse
                  ) * this->dynamicalViscosity
// 3D T_33_z
                + ( 4.0 / 3.0 * ( velocity_z_up * velocity_z_center - velocity_z_center * velocity_z_down
                                - velocity_z_center * velocity_z_center + velocity_z_down * velocity_z_down
                                ) * hzSquareInverse
                  - 2.0 / 3.0 * ( velocity_y_upNorth * velocity_z_up - velocity_y_downNorth * velocity_z_down
                                - velocity_y_upSouth * velocity_z_up + velocity_y_downSouth * velocity_z_down
                                ) * hyInverse * hzInverse / 4
                  - 2.0 / 3.0 * ( velocity_x_upEast * velocity_z_up - velocity_x_downEast * velocity_z_down
                                - velocity_x_upWest * velocity_z_up + velocity_x_downWest * velocity_z_down
                                ) * hxInverse * hzInverse / 4
                  ) * this->dynamicalViscosity;                  
      }

      /*template< typename MeshEntity >
      __cuda_callable__
      Index getLinearSystemRowLength( const MeshType& mesh,
                                      const IndexType& index,
                                      const MeshEntity& entity ) const;

      template< typename MeshEntity, typename Vector, typename MatrixRow >
      __cuda_callable__
      void updateLinearSystem( const RealType& time,
                               const RealType& tau,
                               const MeshType& mesh,
                               const IndexType& index,
                               const MeshEntity& entity,
                               const MeshFunctionType& u,
                               Vector& b,
                               MatrixRow& matrixRow ) const;*/
};

} //namespace TNL
