Stokhos_SymmetricDiagonalSpec.hpp

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#ifndef STOKHOS_SYMMETRIC_DIAGONAL_SPEC_HPP
#define STOKHOS_SYMMETRIC_DIAGONAL_SPEC_HPP
 
#include "Kokkos_StaticCrsGraph.hpp"
 
namespace Stokhos {

template< class ExecutionSpace >
class SymmetricDiagonalSpec {
public:
 
  typedef unsigned size_type;

  KOKKOS_INLINE_FUNCTION
  unsigned dimension() const { return m_dimension ; }

  KOKKOS_INLINE_FUNCTION
  unsigned matrix_offset( const unsigned row , const unsigned column ) const
    {
      const int diag_count = 1 + ( m_dimension >> 1 );
      const int diag = (int) column - (int) row ;
 
      unsigned offset = 0 ;
 
      if ( ( 0 <= diag && diag < diag_count ) || ( diag <= - diag_count ) ) {
        offset = row + m_dimension * ( ( m_dimension + diag ) % m_dimension );
      }
      else {
        offset = column + m_dimension * ( ( m_dimension - diag ) % m_dimension );
      }
 
      return offset ;
    }

  KOKKOS_INLINE_FUNCTION
  unsigned matrix_size() const
    { return ( m_dimension * ( m_dimension + 1 ) ) >> 1 ; }
 
  SymmetricDiagonalSpec()
    : m_dimension( 0 ) {}
 
  SymmetricDiagonalSpec( const SymmetricDiagonalSpec & rhs )
    : m_dimension( rhs.m_dimension ) {}
 
  SymmetricDiagonalSpec & operator =
    ( const SymmetricDiagonalSpec & rhs )
      { m_dimension = rhs.m_dimension ; return *this ; }
 
  explicit
  SymmetricDiagonalSpec( const unsigned dim )
    : m_dimension( dim ) {}
 
private:
  unsigned m_dimension ;
};
 
template < typename Device >
class BlockMultiply< SymmetricDiagonalSpec< Device > > {
public:
  typedef Device execution_space ;
  typedef typename execution_space::size_type size_type ;
  typedef SymmetricDiagonalSpec< execution_space > block_type ;
 
  template< typename MatrixValue , typename VectorValue >
  KOKKOS_INLINE_FUNCTION
  static void apply( const block_type  & block ,
                     const MatrixValue *       a ,
                     const VectorValue * const x ,
                           VectorValue * const y )
  {
    const size_type dimension = block.dimension();
    const size_type dim_half  = ( dimension + 1 ) >> 1 ;
 
    // Multiply the main diagonal (first diagonal)
    for ( size_type j = 0 ; j < dimension ; ++j ) {
      y[j] += a[j] * x[j] ; // Contiguous access
    }
 
    // Multiply remaining full diagionals, each diagonal is accessed twice
    for ( size_type d = 1 ; d < dim_half ; ++d ) {
      size_type kx  = d ;
      size_type kxr = dimension - d ;
 
      a += dimension ; // next diagonal
 
      for ( size_type j = 0 ; j < dimension ; ++j ) {
        y[j] += a[j] * x[kx] + a[kxr] * x[kxr]; // Contiguous access
        if ( dimension == ++kx )  kx = 0 ;
        if ( dimension == ++kxr ) kxr = 0 ;
      }
    }
 
    // If even number of diagonals then the last diagonal is half-length
    if ( ! ( dimension & 01 ) ) {
      size_type kx = dim_half ;
 
      a += dimension ; // next diagonal
 
      for ( size_type j = 0 ; j < dim_half ; ++j , ++kx ) {
        y[j]  += a[j] * x[kx] ; // Contiguous access
        y[kx] += a[j] * x[j] ;  // Contiguous access
      }
    }
  }
 
  KOKKOS_INLINE_FUNCTION
  static size_type matrix_size( const block_type & block )
    { return block.matrix_size(); }
};
 
} // namespace Stokhos
 
#endif /* #ifndef STOKHOS_SYMMETRIC_DIAGONAL_SPEC_HPP */