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fft_utils.hh
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rMUSPECTRE µSpectre
fft_utils.hh
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/**
* @file fft_utils.hh
*
* @author Till Junge <till.junge@epfl.ch>
*
* @date 06 Dec 2017
*
* @brief collection of functions used in the context of spectral operations
*
* 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_UTILS_H
#define FFT_UTILS_H
#include "common/common.hh"
#include <Eigen/Dense>
#include <valarray>
#include <array>
namespace
muSpectre
{
/**
* compute fft frequencies (in time (or length) units of of sampling
* periods), see numpy's fftfreq function for reference
*/
std
::
valarray
<
Real
>
fft_freqs
(
size_t
nb_samples
);
/**
* compute fft frequencies in correct length or time units. Here,
* length refers to the total size of the domain over which the fft
* is taken (for instance the length of an edge of an RVE)
*/
std
::
valarray
<
Real
>
fft_freqs
(
size_t
nb_samples
,
Real
length
);
/**
* Get fft_freqs for a grid
*/
template
<
size_t
dim
>
inline
std
::
array
<
std
::
valarray
<
Real
>
,
dim
>
fft_freqs
(
Ccoord_t
<
dim
>
sizes
,
std
::
array
<
Real
,
dim
>
lengths
)
{
std
::
array
<
std
::
valarray
<
Real
>
,
dim
>
retval
{};
for
(
size_t
i
=
0
;
i
<
dim
;
++
i
)
{
retval
[
i
]
=
std
::
move
(
fft_freqs
(
sizes
[
i
],
lengths
[
i
]));
}
return
retval
;
}
/**
* simple class encapsulating the creation, and retrieval of
* wave vectors
*/
template
<
Dim_t
dim
>
class
FFT_freqs
{
public
:
//! return type for wave vectors
using
Vector
=
Eigen
::
Matrix
<
Real
,
dim
,
1
>
;
//! Default constructor
FFT_freqs
()
=
delete
;
//! constructor with problem sizes
FFT_freqs
(
Ccoord_t
<
dim
>
sizes
,
std
::
array
<
Real
,
dim
>
lengths
)
:
freqs
{
fft_freqs
(
sizes
,
lengths
)}
{}
//! Copy constructor
FFT_freqs
(
const
FFT_freqs
&
other
)
=
delete
;
//! Move constructor
FFT_freqs
(
FFT_freqs
&&
other
)
=
default
;
//! Destructor
virtual
~
FFT_freqs
()
=
default
;
//! Copy assignment operator
FFT_freqs
&
operator
=
(
const
FFT_freqs
&
other
)
=
delete
;
//! Move assignment operator
FFT_freqs
&
operator
=
(
FFT_freqs
&&
other
)
=
default
;
//! get unnormalised wave vector (in sampling units)
inline
Vector
get_xi
(
const
Ccoord_t
<
dim
>
ccoord
)
const
;
//! get normalised wave vector
inline
Vector
get_unit_xi
(
const
Ccoord_t
<
dim
>
ccoord
)
const
{
auto
&&
xi
=
this
->
get_xi
(
std
::
move
(
ccoord
));
return
xi
/
xi
.
norm
();
}
protected
:
//! container for frequencies ordered by spatial dimension
const
std
::
array
<
std
::
valarray
<
Real
>
,
dim
>
freqs
;
private
:
};
template
<
Dim_t
dim
>
typename
FFT_freqs
<
dim
>::
Vector
FFT_freqs
<
dim
>::
get_xi
(
const
Ccoord_t
<
dim
>
ccoord
)
const
{
Vector
retval
{};
for
(
Dim_t
i
=
0
;
i
<
dim
;
++
i
)
{
retval
(
i
)
=
this
->
freqs
[
i
][
ccoord
[
i
]];
}
return
retval
;
}
}
// muSpectre
#endif
/* FFT_UTILS_H */
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