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tamaas/src/core/fftransform.hh
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fftransform.hh
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/**
* @file
* @section LICENSE
*
* Copyright (©) 2016-2020 EPFL (École Polytechnique Fédérale de Lausanne),
* Laboratory (LSMS - Laboratoire de Simulation en Mécanique des Solides)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published
* by the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*
*/
/* -------------------------------------------------------------------------- */
#ifndef FFTRANSFORM_HH
#define FFTRANSFORM_HH
/* -------------------------------------------------------------------------- */
#include "grid.hh"
#include "grid_hermitian.hh"
#include "tamaas.hh"
#include "static_types.hh"
#include <thrust/execution_policy.h>
#include <vector>
/* -------------------------------------------------------------------------- */
namespace tamaas {
/* -------------------------------------------------------------------------- */
/**
* @brief Generic class for FFT interface wrapping
*/
template <typename T, UInt dim>
class FFTransform {
public:
/// Constructor
FFTransform(Grid<T, dim>& real, GridHermitian<T, dim>& spectral);
/// Destructor
virtual ~FFTransform();
public:
/// Perform FFT
virtual void forwardTransform() = 0;
/// Perform IFFT
virtual void backwardTransform() = 0;
/// Normalize the real surface after backward transform
virtual void normalize();
public:
/// Fill a grid with modevectors: boolean if grid has hermitian dimensions
template <bool hermitian>
static Grid<T, dim> computeFrequencies(const std::array<UInt, dim>& sizes);
protected:
Grid<T, dim> real;
GridHermitian<T, dim> spectral;
};
/* -------------------------------------------------------------------------- */
template <typename T, UInt dim>
template <bool hermitian>
Grid<T, dim>
FFTransform<T, dim>::computeFrequencies(const std::array<UInt, dim>& sizes) {
// If hermitian is true, we suppose the dimensions of freq are
// reduced based on hermitian symetry and that it has dim components
auto& n = sizes;
Grid<T, dim> freq(n, dim);
constexpr UInt dmax = dim - static_cast<UInt>(hermitian);
#pragma omp parallel for // to get rid of a compilation warning from nvcc
for (UInt i = 0; i < freq.getNbPoints(); ++i) {
UInt index = i;
VectorProxy<T, dim> wavevector(freq(index * freq.getNbComponents()));
std::array<UInt, dim> tuple{{0}};
/// Computing tuple from index
for (Int d = dim - 1; d >= 0; d--) {
tuple[d] = index % n[d];
index -= tuple[d];
index /= n[d];
}
if (hermitian)
wavevector(dim - 1) = tuple[dim - 1];
for (UInt d = 0; d < dmax; d++) {
// Type conversion
T td = tuple[d];
T nd = n[d];
T q = (tuple[d] < n[d] / 2) ? td : td - nd;
wavevector(d) = q;
}
}
return freq;
}
/* -------------------------------------------------------------------------- */
} // namespace tamaas
/* -------------------------------------------------------------------------- */
#endif // FFTRANSFORM_HH
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