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fft_engine_base.hh
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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 */

muSpectre/src/fft/fft_engine_base.hh1c871f98ffb7intersection_octree

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muSpectre/src/fft/fft_engine_base.hh
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fft_engine_base.hh
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