fft.hpp File Reference

Routines, row decomposition, data structures and communication for the 3D-FFT. More...

#include "config/config.hpp"
#include <utils/Vector.hpp>
#include <boost/mpi/communicator.hpp>
#include <fftw3.h>
#include <cstddef>
#include <new>
#include <vector>

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Classes
struct	fft_allocator< T >
	Aligned allocator for fft data. More...
struct	fft_forw_plan
	Structure for performing a 1D FFT. More...
struct	fft_back_plan
	Additional information for backwards FFT. More...
struct	fft_data_struct
	Information about the three one dimensional FFTs and how the nodes have to communicate inbetween. More...

Typedefs
template<class T >
using	fft_vector = std::vector< T, fft_allocator< T > >

Functions
int	fft_init (Utils::Vector3i const &ca_mesh_dim, int const *ca_mesh_margin, Utils::Vector3i const &global_mesh_dim, Utils::Vector3d const &global_mesh_off, int &ks_pnum, fft_data_struct &fft, Utils::Vector3i const &grid, boost::mpi::communicator const &comm)
	Initialize everything connected to the 3D-FFT.
void	fft_perform_forw (double *data, fft_data_struct &fft, const boost::mpi::communicator &comm)
	Perform an in-place forward 3D FFT.
void	fft_perform_back (double *data, bool check_complex, fft_data_struct &fft, const boost::mpi::communicator &comm)
	Perform an in-place backward 3D FFT.
void	fft_pack_block (double const *in, double *out, int const start[3], int const size[3], int const dim[3], int element)
	Pack a block (size[3] starting at start[3]) of an input 3d-grid with dimension dim[3] into an output 3d-block with dimension size[3].
void	fft_unpack_block (double const *in, double *out, int const start[3], int const size[3], int const dim[3], int element)
	Unpack a 3d-grid input block (size[3]) into an output 3d-grid with dimension dim[3] at start position start[3].

Detailed Description

Routines, row decomposition, data structures and communication for the 3D-FFT.

The 3D-FFT is split into 3 ond dimensional FFTs. The data is distributed in such a way, that for the actual direction of the FFT each node has a certain number of rows for which it performs a 1D-FFT. After performing the FFT on that direction the data is redistributed.

For simplicity at the moment I have implemented a full complex to complex FFT (even though a real to complex FFT would be sufficient)

Todo:

Combine the forward and backward structures.

The packing routines could be moved to utils.hpp when they are needed elsewhere.

For more information about FFT usage, see fft.cpp.

Definition in file fft.hpp.

Typedef Documentation

fft_vector

template<class T >

using fft_vector = std::vector<T, fft_allocator<T> >

Definition at line 87 of file fft.hpp.

Function Documentation

fft_init()

int fft_init	(	Utils::Vector3i const &	ca_mesh_dim,
		int const *	ca_mesh_margin,
		Utils::Vector3i const &	global_mesh_dim,
		Utils::Vector3d const &	global_mesh_off,
		int &	ks_pnum,
		fft_data_struct &	fft,
		Utils::Vector3i const &	grid,
		boost::mpi::communicator const &	comm
	)

Initialize everything connected to the 3D-FFT.

Parameters

[in]	ca_mesh_dim	Local CA mesh dimensions.
[in]	ca_mesh_margin	Local CA mesh margins.
[in]	global_mesh_dim	Global CA mesh dimensions.
[in]	global_mesh_off	Global CA mesh offset.
[out]	ks_pnum	Number of permutations in k-space.
[out]	fft	FFT plan.
[in]	grid	Number of nodes in each spatial dimension.
[in]	comm	MPI communicator.

Returns

Maximal size of local fft mesh (needed for allocation of ca_mesh).

Definition at line 483 of file fft.cpp.

References fft_data_struct::back, anonymous_namespace{fft.cpp}::calc_2d_grid(), anonymous_namespace{fft.cpp}::calc_local_mesh(), anonymous_namespace{fft.cpp}::calc_send_block(), Utils::Array< T, N >::data(), fft_data_struct::data_buf, fft_forw_plan::dir, fft_back_plan::dir, fft_forw_plan::element, fft_pack_block(), anonymous_namespace{fft.cpp}::find_comm_groups(), fft_forw_plan::group, fft_data_struct::init_tag, Utils::make_span(), anonymous_namespace{fft.cpp}::map_3don2d_grid(), fft_data_struct::max_comm_size, fft_data_struct::max_mesh_size, fft_forw_plan::n_ffts, fft_forw_plan::n_permute, fft_forw_plan::new_mesh, fft_forw_plan::new_size, node, fft_forw_plan::old_mesh, fft_forw_plan::our_fftw_plan, fft_back_plan::our_fftw_plan, anonymous_namespace{fft.cpp}::pack_block_permute1(), anonymous_namespace{fft.cpp}::pack_block_permute2(), fft_forw_plan::pack_function, fft_back_plan::pack_function, fft_data_struct::plan, Utils::product(), fft_forw_plan::recv_block, fft_data_struct::recv_buf, fft_forw_plan::recv_size, fft_forw_plan::row_dir, fft_forw_plan::send_block, fft_data_struct::send_buf, fft_forw_plan::send_size, and fft_forw_plan::start.

Referenced by CoulombP3M::init(), and DipolarP3M::init().

fft_pack_block()

void fft_pack_block	(	double const *	in,
		double *	out,
		int const	start[3],
		int const	size[3],
		int const	dim[3],
		int	element
	)

Pack a block (size[3] starting at start[3]) of an input 3d-grid with dimension dim[3] into an output 3d-block with dimension size[3].

The block with dimensions (size[0], size[1], size[2]) is stored in 'row-major-order' or 'C-order', that means the first index is changing slowest when running through the linear array. The element (i0 (slow), i1 (mid), i2 (fast)) has the linear index li = i2 + size[2] * (i1 + (size[1] * i0)).

Parameters

[in]	in	pointer to input 3d-grid.
[out]	out	pointer to output 3d-grid (block).
[in]	start	start index of the block in the in-grid.
[in]	size	size of the block (=dimension of the out-grid).
[in]	dim	size of the in-grid.
[in]	element	size of a grid element (e.g. 1 for Real, 2 for Complex).

Definition at line 755 of file fft.cpp.

Referenced by fft_init(), p3m_send_mesh::gather_grid(), and p3m_send_mesh::spread_grid().

fft_perform_back()

void fft_perform_back	(	double *	data,
		bool	check_complex,
		fft_data_struct &	fft,
		const boost::mpi::communicator &	comm
	)

Perform an in-place backward 3D FFT.

Warning

The content of data is overwritten.

Parameters

[in,out]	data	Mesh.
[in]	check_complex	Throw an error if the complex component is non-zero.
[in,out]	fft	FFT plan.
[in]	comm	MPI communicator.

Definition at line 713 of file fft.cpp.

References fft_data_struct::back, anonymous_namespace{fft.cpp}::back_grid_comm(), fft_data_struct::data_buf, fft_forw_plan::new_size, fft_back_plan::our_fftw_plan, and fft_data_struct::plan.

Referenced by CoulombP3M::long_range_kernel(), and DipolarP3M::long_range_kernel().

fft_perform_forw()

void fft_perform_forw	(	double *	data,
		fft_data_struct &	fft,
		const boost::mpi::communicator &	comm
	)

Perform an in-place forward 3D FFT.

Warning

The content of data is overwritten.

Parameters

[in,out]	data	Mesh.
[in,out]	fft	FFT plan.
[in]	comm	MPI communicator

Definition at line 682 of file fft.cpp.

References fft_data_struct::data_buf, anonymous_namespace{fft.cpp}::forw_grid_comm(), fft_forw_plan::new_size, fft_forw_plan::our_fftw_plan, and fft_data_struct::plan.

Referenced by CoulombP3M::long_range_kernel(), DipolarP3M::long_range_kernel(), and CoulombP3M::long_range_pressure().

fft_unpack_block()

void fft_unpack_block	(	double const *	in,
		double *	out,
		int const	start[3],
		int const	size[3],
		int const	dim[3],
		int	element
	)

Unpack a 3d-grid input block (size[3]) into an output 3d-grid with dimension dim[3] at start position start[3].

see also fft_pack_block.

Parameters

[in]	in	pointer to input 3d-grid.
[out]	out	pointer to output 3d-grid (block).
[in]	start	start index of the block in the in-grid.
[in]	size	size of the block (=dimension of the out-grid).
[in]	dim	size of the in-grid.
[in]	element	size of a grid element (e.g. 1 for Real, 2 for Complex).

Definition at line 779 of file fft.cpp.

Referenced by anonymous_namespace{fft.cpp}::back_grid_comm(), anonymous_namespace{fft.cpp}::forw_grid_comm(), and p3m_send_mesh::spread_grid().