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fft_engine.hh
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fft_engine.hh
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/*
* SPDX-License-Indentifier: AGPL-3.0-or-later
*
* Copyright (©) 2016-2024 EPFL (École Polytechnique Fédérale de Lausanne),
* Laboratory (LSMS - Laboratoire de Simulation en Mécanique des Solides)
* Copyright (©) 2020-2024 Lucas Frérot
*
* 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 FFT_ENGINE_H
#define FFT_ENGINE_H
/* -------------------------------------------------------------------------- */
#include "grid.hh"
#include "grid_base.hh"
#include "grid_hermitian.hh"
#include "partitioner.hh"
#include <algorithm>
#include <array>
#include <map>
#include <memory>
#include <string>
/* -------------------------------------------------------------------------- */
namespace tamaas {
class FFTEngine {
protected:
using key_t = std::basic_string<UInt>;
public:
virtual ~FFTEngine() noexcept = default;
/// Execute a forward plan on real and spectral 1D
virtual void forward(const Grid<Real, 1>& real,
GridHermitian<Real, 1>& spectral) = 0;
/// Execute a forward plan on real and spectral 2D
virtual void forward(const Grid<Real, 2>& real,
GridHermitian<Real, 2>& spectral) = 0;
/// Execute a backward plan on real and spectral 1D
virtual void backward(Grid<Real, 1>& real,
GridHermitian<Real, 1>& spectral) = 0;
/// Execute a backward plan on real and spectral 2D
virtual void backward(Grid<Real, 2>& real,
GridHermitian<Real, 2>& spectral) = 0;
/// Fill a grid with wavevector values in appropriate ordering
template <typename T, UInt dim, bool hermitian>
static Grid<T, dim> computeFrequencies(const std::array<UInt, dim>& sizes);
/// Return the grid indices that contain real coefficients (see R2C transform)
template <UInt dim>
static std::vector<std::array<UInt, dim>>
realCoefficients(const std::array<UInt, dim>& sizes);
/// Instanciate an appropriate FFTEngine subclass
static std::unique_ptr<FFTEngine>
makeEngine(unsigned int flags = FFTW_ESTIMATE);
protected:
/// Make a transform signature from a pair of grids
template <UInt dim>
static key_t make_key(const Grid<Real, dim>& real,
const GridHermitian<Real, dim>& spectral);
};
template <UInt dim>
FFTEngine::key_t FFTEngine::make_key(const Grid<Real, dim>& real,
const GridHermitian<Real, dim>& spectral) {
TAMAAS_ASSERT(real.getNbComponents() == spectral.getNbComponents(),
"Components do not match");
auto hermitian_dims =
GridHermitian<Real, dim>::hermitianDimensions(real.sizes());
TAMAAS_ASSERT(std::equal(hermitian_dims.begin(), hermitian_dims.end(),
spectral.sizes().begin()),
"Spectral grid does not have hermitian size");
// Reserve space for dimensions + components + both last strides
key_t key(real.getDimension() + 3, 0);
std::copy_n(real.sizes().begin(), dim, key.begin());
key[dim] = real.getNbComponents();
key[dim + 1] = real.getStrides().back();
key[dim + 2] = spectral.getStrides().back();
return key;
}
template <typename T, UInt dim, bool hermitian>
Grid<T, dim>
FFTEngine::computeFrequencies(const std::array<UInt, dim>& local_sizes) {
// If hermitian is true, we suppose the dimensions of freq are
// reduced based on hermitian symetry and that it has dim components
Grid<T, dim> freq(local_sizes, dim);
constexpr Int dmax = dim - static_cast<Int>(hermitian);
// For MPI
const auto& n = Partitioner<dim>::global_size(local_sizes);
const auto offset = Partitioner<dim>::local_offset(freq) / dim;
#pragma omp parallel for // to get rid of a compilation warning from nvcc
for (UInt i = 0; i < freq.getNbPoints(); ++i) {
UInt index = i + offset;
VectorProxy<T, dim> wavevector(freq(i * 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 (Int 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

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