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#include <WarpXConst.H>
#include <SpectralKSpace.H>
SpectralKSpace::SpectralKSpace( const BoxArray& realspace_ba,
const DistributionMapping& dm,
const Real* realspace_dx )
{
// Create the box array that corresponds to spectral space
BoxList spectral_bl; // Create empty box list
// Loop over boxes and fill the box list
for (int i=0; i < realspace_ba.size(); i++ ) {
// For local FFTs, each box in spectral space starts at 0 in each direction
// and has the same number of points as the real space box (including guard cells)
Box realspace_bx = realspace_ba[i];
Box bx = Box( IntVect::TheZeroVector(), realspace_bx.bigEnd() - realspace_bx.smallEnd() );
spectral_bl.push_back( bx );
}
spectralspace_ba.define( spectral_bl );
// Allocate the 1D vectors
kx_vec = SpectralKVector( spectralspace_ba, dm );
ky_vec = SpectralKVector( spectralspace_ba, dm );
kz_vec = SpectralKVector( spectralspace_ba, dm );
// Initialize the values on each box
for ( MFIter mfi(spectralspace_ba, dm); mfi.isValid(); ++mfi ){
Box bx = spectralspace_ba[mfi];
AllocateAndFillKvector( kx_vec[mfi], bx, dx, 0 );
AllocateAndFillKvector( ky_vec[mfi], bx, dx, 1 );
AllocateAndFillKvector( kz_vec[mfi], bx, dx, 2 );
}
// Store the cell size
dx = realspace_dx;
}
void
AllocateAndFillKvector( ManagedVector<Real>& k, const Box& bx, const Real* dx, const int i_dim )
{
// Alllocate k to the right size
int N = bx.length( i_dim );
k.resize( N );
// Fill the k vector
const Real dk = 2*MathConst::pi/(N*dx[i_dim]);
AMREX_ALWAYS_ASSERT_WITH_MESSAGE( bx.smallEnd(i_dim) == 0,
"Expected box to start at 0, in spectral space.");
AMREX_ALWAYS_ASSERT_WITH_MESSAGE( bx.bigEnd(i_dim) == N-1,
"Expected different box end index in spectral space.");
// Fill positive values of k (FFT conventions: first half is positive)
for (int i=0; i<(N+1)/2; i++ ){
k[i] = i*dk;
}
// Fill negative values of k (FFT conventions: second half is negative)
for (int i=(N+1)/2; i<N; i++){
k[i] = (N-i)*dk;
}
// TODO: This should be quite different for the hybrid spectral code:
// In that case we should take into consideration the actual indices of the box
// and distinguish the size of the local box and that of the global FFT
// TODO: For real-to-complex,
}
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