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#include <SpectralFieldData.H>
using namespace amrex;
/* \brief Initialize fields in spectral space, and FFT plans */
SpectralFieldData::SpectralFieldData( const BoxArray& realspace_ba,
const SpectralKSpace& k_space,
const DistributionMapping& dm,
const int n_field_required )
{
const BoxArray& spectralspace_ba = k_space.spectralspace_ba;
// Allocate the arrays that contain the fields in spectral space
// (one component per field)
fields = SpectralField(spectralspace_ba, dm, n_field_required, 0);
// Allocate temporary arrays - in real space and spectral space
// These arrays will store the data just before/after the FFT
tmpRealField = MultiFab(realspace_ba, dm, 1, 0);
tmpSpectralField = SpectralField(spectralspace_ba, dm, 1, 0);
// By default, we assume the FFT is done from/to a nodal grid in real space
// It the FFT is performed from/to a cell-centered grid in real space,
// a correcting "shift" factor must be applied in spectral space.
xshift_FFTfromCell = k_space.getSpectralShiftFactor(dm, 0,
ShiftType::TransformFromCellCentered);
xshift_FFTtoCell = k_space.getSpectralShiftFactor(dm, 0,
ShiftType::TransformToCellCentered);
#if (AMREX_SPACEDIM == 3)
yshift_FFTfromCell = k_space.getSpectralShiftFactor(dm, 1,
ShiftType::TransformFromCellCentered);
yshift_FFTtoCell = k_space.getSpectralShiftFactor(dm, 1,
ShiftType::TransformToCellCentered);
zshift_FFTfromCell = k_space.getSpectralShiftFactor(dm, 2,
ShiftType::TransformFromCellCentered);
zshift_FFTtoCell = k_space.getSpectralShiftFactor(dm, 2,
ShiftType::TransformToCellCentered);
#else
zshift_FFTfromCell = k_space.getSpectralShiftFactor(dm, 1,
ShiftType::TransformFromCellCentered);
zshift_FFTtoCell = k_space.getSpectralShiftFactor(dm, 1,
ShiftType::TransformToCellCentered);
#endif
// Allocate and initialize the FFT plans
forward_plan = FFTplans(spectralspace_ba, dm);
backward_plan = FFTplans(spectralspace_ba, dm);
// Loop over boxes and allocate the corresponding plan
// for each box owned by the local MPI proc
for ( MFIter mfi(spectralspace_ba, dm); mfi.isValid(); ++mfi ){
// Note: the size of the real-space box and spectral-space box
// differ when using real-to-complex FFT. When initializing
// the FFT plan, the valid dimensions are those of the real-space box.
IntVect fft_size = realspace_ba[mfi].length();
#ifdef AMREX_USE_GPU
// Add cuFFT-specific code
#else
// Create FFTW plans
forward_plan[mfi] =
// Swap dimensions: AMReX FAB are Fortran-order but FFTW is C-order
#if (AMREX_SPACEDIM == 3)
fftw_plan_dft_r2c_3d( fft_size[2], fft_size[1], fft_size[0],
#else
fftw_plan_dft_r2c_2d( fft_size[1], fft_size[0],
#endif
tmpRealField[mfi].dataPtr(),
reinterpret_cast<fftw_complex*>( tmpSpectralField[mfi].dataPtr() ),
FFTW_ESTIMATE );
backward_plan[mfi] =
// Swap dimensions: AMReX FAB are Fortran-order but FFTW is C-order
#if (AMREX_SPACEDIM == 3)
fftw_plan_dft_c2r_3d( fft_size[2], fft_size[1], fft_size[0],
#else
fftw_plan_dft_c2r_2d( fft_size[1], fft_size[0],
#endif
reinterpret_cast<fftw_complex*>( tmpSpectralField[mfi].dataPtr() ),
tmpRealField[mfi].dataPtr(),
FFTW_ESTIMATE );
#endif
}
}
SpectralFieldData::~SpectralFieldData()
{
if (tmpRealField.size() > 0){
for ( MFIter mfi(tmpRealField); mfi.isValid(); ++mfi ){
#ifdef AMREX_USE_GPU
// Add cuFFT-specific code
#else
// Destroy FFTW plans
fftw_destroy_plan( forward_plan[mfi] );
fftw_destroy_plan( backward_plan[mfi] );
#endif
}
}
}
/* \brief Transform the component `i_comp` of MultiFab `mf`
* to spectral space, and store the corresponding result internally
* (in the spectral field specified by `field_index`) */
void
SpectralFieldData::ForwardTransform( const MultiFab& mf,
const int field_index,
const int i_comp )
{
// Check field index type, in order to apply proper shift in spectral space
const bool is_nodal_x = mf.is_nodal(0);
#if (AMREX_SPACEDIM == 3)
const bool is_nodal_y = mf.is_nodal(1);
const bool is_nodal_z = mf.is_nodal(2);
#else
const bool is_nodal_z = mf.is_nodal(1);
#endif
// Loop over boxes
for ( MFIter mfi(mf); mfi.isValid(); ++mfi ){
// Copy the real-space field `mf` to the temporary field `tmpRealField`
// This ensures that all fields have the same number of points
// before the Fourier transform.
// As a consequence, the copy discards the *last* point of `mf`
// in any direction that has *nodal* index type.
{
Box realspace_bx = mf[mfi].box(); // Copy the box
realspace_bx.enclosedCells(); // Discard last point in nodal direction
AMREX_ALWAYS_ASSERT( realspace_bx == tmpRealField[mfi].box() );
Array4<const Real> mf_arr = mf[mfi].array();
Array4<Real> tmp_arr = tmpRealField[mfi].array();
ParallelFor( realspace_bx,
[=] AMREX_GPU_DEVICE(int i, int j, int k) noexcept {
tmp_arr(i,j,k) = mf_arr(i,j,k,i_comp);
});
}
// Perform Fourier transform from `tmpRealField` to `tmpSpectralField`
#ifdef AMREX_USE_GPU
// Add cuFFT-specific code ; make sure that this is done on the same
// GPU stream as the above copy
#else
fftw_execute( forward_plan[mfi] );
#endif
// Copy the spectral-space field `tmpSpectralField` to the appropriate
// index of the FabArray `fields` (specified by `field_index`)
// and apply correcting shift factor if the real space data comes
// from a cell-centered grid in real space instead of a nodal grid.
{
Array4<Complex> fields_arr = SpectralFieldData::fields[mfi].array();
Array4<const Complex> tmp_arr = tmpSpectralField[mfi].array();
const Complex* xshift_arr = xshift_FFTfromCell[mfi].dataPtr();
#if (AMREX_SPACEDIM == 3)
const Complex* yshift_arr = yshift_FFTfromCell[mfi].dataPtr();
#endif
const Complex* zshift_arr = zshift_FFTfromCell[mfi].dataPtr();
// Loop over indices within one box
const Box spectralspace_bx = tmpSpectralField[mfi].box();
ParallelFor( spectralspace_bx,
[=] AMREX_GPU_DEVICE(int i, int j, int k) noexcept {
Complex spectral_field_value = tmp_arr(i,j,k);
// Apply proper shift in each dimension
if (is_nodal_x==false) spectral_field_value *= xshift_arr[i];
#if (AMREX_SPACEDIM == 3)
if (is_nodal_y==false) spectral_field_value *= yshift_arr[j];
if (is_nodal_z==false) spectral_field_value *= zshift_arr[k];
#elif (AMREX_SPACEDIM == 2)
if (is_nodal_z==false) spectral_field_value *= zshift_arr[j];
#endif
// Copy field into the right index
fields_arr(i,j,k,field_index) = spectral_field_value;
});
}
}
}
/* \brief Transform spectral field specified by `field_index` back to
* real space, and store it in the component `i_comp` of `mf` */
void
SpectralFieldData::BackwardTransform( MultiFab& mf,
const int field_index,
const int i_comp )
{
// Check field index type, in order to apply proper shift in spectral space
const bool is_nodal_x = mf.is_nodal(0);
#if (AMREX_SPACEDIM == 3)
const bool is_nodal_y = mf.is_nodal(1);
const bool is_nodal_z = mf.is_nodal(2);
#else
const bool is_nodal_z = mf.is_nodal(1);
#endif
// Loop over boxes
for ( MFIter mfi(mf); mfi.isValid(); ++mfi ){
// Copy the spectral-space field `tmpSpectralField` to the appropriate
// field (specified by the input argument field_index)
// and apply correcting shift factor if the field is to be transformed
// to a cell-centered grid in real space instead of a nodal grid.
{
Array4<const Complex> field_arr = SpectralFieldData::fields[mfi].array();
Array4<Complex> tmp_arr = tmpSpectralField[mfi].array();
const Complex* xshift_arr = xshift_FFTtoCell[mfi].dataPtr();
#if (AMREX_SPACEDIM == 3)
const Complex* yshift_arr = yshift_FFTtoCell[mfi].dataPtr();
#endif
const Complex* zshift_arr = zshift_FFTtoCell[mfi].dataPtr();
// Loop over indices within one box
const Box spectralspace_bx = tmpSpectralField[mfi].box();
ParallelFor( spectralspace_bx,
[=] AMREX_GPU_DEVICE(int i, int j, int k) noexcept {
Complex spectral_field_value = field_arr(i,j,k,field_index);
// Apply proper shift in each dimension
if (is_nodal_x==false) spectral_field_value *= xshift_arr[i];
#if (AMREX_SPACEDIM == 3)
if (is_nodal_y==false) spectral_field_value *= yshift_arr[j];
if (is_nodal_z==false) spectral_field_value *= zshift_arr[k];
#elif (AMREX_SPACEDIM == 2)
if (is_nodal_z==false) spectral_field_value *= zshift_arr[j];
#endif
// Copy field into temporary array
tmp_arr(i,j,k) = spectral_field_value;
});
}
// Perform Fourier transform from `tmpSpectralField` to `tmpRealField`
#ifdef AMREX_USE_GPU
// Add cuFFT-specific code ; make sure that this is done on the same
// GPU stream as the above copy
#else
fftw_execute( backward_plan[mfi] );
#endif
// Copy the temporary field `tmpRealField` to the real-space field `mf`
// Normalize (divide by 1/N) since the FFT+IFFT results in a factor N
{
const Box realspace_bx = tmpRealField[mfi].box();
Array4<Real> mf_arr = mf[mfi].array();
Array4<const Real> tmp_arr = tmpRealField[mfi].array();
// Normalization: divide by the number of points in realspace
const Real inv_N = 1./realspace_bx.numPts();
ParallelFor( realspace_bx,
[=] AMREX_GPU_DEVICE(int i, int j, int k) noexcept {
// Copy and normalize field
mf_arr(i,j,k,i_comp) = inv_N*tmp_arr(i,j,k);
});
}
}
}
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