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fft_engine_base.hh
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/**
* @file fft_engine_base.hh
*
* @author Till Junge <till.junge@epfl.ch>
*
* @date 01 Dec 2017
*
* @brief Interface for FFT engines
*
* Copyright © 2017 Till Junge
*
* µSpectre is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation, either version 3, or (at
* your option) any later version.
*
* µSpectre 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Emacs; see the file COPYING. If not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#ifndef FFT_ENGINE_BASE_H
#define FFT_ENGINE_BASE_H
#include "common/common.hh"
#include "common/field_collection.hh"
namespace muSpectre {
/**
* Virtual base class for FFT engines. To be implemented by all
* FFT_engine implementations.
*/
template <Dim_t DimS, Dim_t DimM>
class FFT_Engine_base
{
public:
constexpr static Dim_t sdim{DimS}; //!< spatial dimension of the cell
constexpr static Dim_t mdim{DimM}; //!< material dimension of the cell
//! cell coordinates type
using Ccoord = Ccoord_t<DimS>;
//! spatial coordinates type
using Rcoord = std::array<Real, DimS>;
//! global FieldCollection
using GFieldCollection_t = FieldCollection<DimS, DimM, true>;
//! local FieldCollection (for Fourier-space pixels)
using LFieldCollection_t = FieldCollection<DimS, DimM, false>;
//! Field type on which to apply the projection
using Field_t = TensorField<GFieldCollection_t, Real, 2, DimM>;
/**
* Field type holding a Fourier-space representation of a
* real-valued second-order tensor field
*/
using Workspace_t = TensorField<LFieldCollection_t, Complex, 2, DimM>;
/**
* iterator over Fourier-space discretisation point
*/
using iterator = typename LFieldCollection_t::iterator;
//! Default constructor
FFT_Engine_base() = delete;
//! Constructor with system resolutions
FFT_Engine_base(Ccoord resolutions, Rcoord lengths);
//! Copy constructor
FFT_Engine_base(const FFT_Engine_base &other) = delete;
//! Move constructor
FFT_Engine_base(FFT_Engine_base &&other) = default;
//! Destructor
virtual ~FFT_Engine_base() = default;
//! Copy assignment operator
FFT_Engine_base& operator=(const FFT_Engine_base &other) = delete;
//! Move assignment operator
FFT_Engine_base& operator=(FFT_Engine_base &&other) = default;
//! compute the plan, etc
virtual void initialise(FFT_PlanFlags /*plan_flags*/);
//! forward transform (dummy for interface)
virtual Workspace_t & fft(Field_t & /*field*/) = 0;
//! inverse transform (dummy for interface)
virtual void ifft(Field_t & /*field*/) const = 0;
/**
* iterators over only those pixels that exist in frequency space
* (i.e. about half of all pixels, see rfft)
*/
//! returns an iterator to the first pixel in Fourier space
inline iterator begin() {return this->work_space_container.begin();}
//! returns an iterator past to the last pixel in Fourier space
inline iterator end() {return this->work_space_container.end();}
//! nb of pixels (mostly for debugging)
size_t size() const;
//! nb of pixels in Fourier space
size_t workspace_size() const;
//! returns the resolutions of the cell
const Ccoord & get_resolutions() const {return this->resolutions;}
//! returns the physical sizes of the cell
const Rcoord & get_lengths() const {return this->lengths;}
//! only required for testing and debugging
LFieldCollection_t & get_field_collection() {
return this->work_space_container;}
//! only required for testing and debugging
Workspace_t& get_work_space() {return this->work;}
//! factor by which to multiply projection before inverse transform (this is
//! typically 1/nb_pixels for so-called unnormalized transforms (see,
//! e.g. http://www.fftw.org/fftw3_doc/Multi_002dDimensional-DFTs-of-Real-Data.html#Multi_002dDimensional-DFTs-of-Real-Data
//! or https://docs.scipy.org/doc/numpy-1.13.0/reference/routines.fft.html
//! . Rather than scaling the inverse transform (which would cost one more
//! loop), FFT engines provide this value so it can be used in the
//! projection operator (where no additional loop is required)
inline Real normalisation() const {return norm_factor;};
protected:
/**
* Field collection in which to store fields associated with
* Fourier-space points
*/
LFieldCollection_t work_space_container{};
const Ccoord resolutions; //!< resolutions of the cell
const Rcoord lengths; //!< physical sizes of the cell
Workspace_t & work; //!< field to store the Fourier transform of P
const Real norm_factor; //!< normalisation coefficient of fourier transform
private:
};
} // muSpectre
#endif /* FFT_ENGINE_BASE_H */

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