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rMUSPECTRE µSpectre
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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