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fftransform.hh
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/**
* @file
*
* @author Lucas Frérot <lucas.frerot@epfl.ch>
*
* @section LICENSE
*
* Copyright (©) 2016 EPFL (Ecole Polytechnique Fédérale de
* Lausanne) Laboratory (LSMS - Laboratoire de Simulation en Mécanique des
* Solides)
*
* Tamaas is free software: you can redistribute it and/or modify it under the
* terms of the GNU Lesser General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option) any
* later version.
*
* Tamaas 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 Lesser General Public License for more
* details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with Tamaas. If not, see <http://www.gnu.org/licenses/>.
*
*/
/* -------------------------------------------------------------------------- */
#ifndef FFTRANSFORM_HH
#define FFTRANSFORM_HH
/* -------------------------------------------------------------------------- */
#include "tamaas.hh"
#include "grid.hh"
#include "grid_hermitian.hh"
#include "types.hh"
#include <vector>
/* -------------------------------------------------------------------------- */
__BEGIN_TAMAAS__
/* -------------------------------------------------------------------------- */
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);
std::array<UInt, dim> tuple = {0};
#pragma omp parallel for firstprivate(tuple)
for (auto it = freq.begin(dim) ; it < freq.end(dim) ; ++it) {
VectorProxy<T> wavevector(&(*it), dim);
UInt index = freq.getNbPoints() - (freq.end(dim) - it);
/// Computing tuple from index
for (UInt d = dim-1 ; d > 0 ; d--) {
tuple[d] = index % n[d];
index -= tuple[d];
index /= n[d];
}
tuple[0] = index;
UInt dmax = dim;
if (hermitian) {
dmax = dim - 1;
wavevector(dim-1) = tuple[dim-1];
}
for (UInt d = 0 ; d < dmax ; d++) {
T td = tuple[d];
T nd = n[d];
T q = (tuple[d] <= n[d]/2) ? td : td-nd;
wavevector(d) = q;
}
}
return freq;
}
/* -------------------------------------------------------------------------- */
__END_TAMAAS__
/* -------------------------------------------------------------------------- */
#endif // FFTRANSFORM_HH

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