fft_work – GS2

Provides some wrappers for managing FFTW plans.

The initialisation routines (init_crfftw, init_rcfftw, init_ccfftw) create FFTW plans, storing them in an instance of fft_type, along with some useful metadata, notably scale.

Uses

- iso_c_binding
- fft_wrapper

Variables

measure_plan time_fft initialised

Interfaces

init_crfftw init_rcfftw

Derived Types

fft_type

Functions

fftw_flags

Subroutines

execute_c2c execute_r2c execute_c2r delete_fft init_fft_work basic_init init_z init_ccfftw init_rcfftw_1d init_crfftw_1d init_rcfftw_2d init_crfftw_2d finish_fft_work save_wisdom load_wisdom

Variables

Type	Visibility		Name		Initial
logical,	public	::	measure_plan	=	.true.	If true, then use FFTW_PATIENT to pick the optimal 42 algorithm, otherwise use FFTW_ESTIMATE (potentially slower but more reproducible results). FFTW_PATIENT takes longer to set up the plan initially, but may be faster overall.
real,	public	::	time_fft(2)	=	0.	Total time taken setting up and performing FFTs
logical,	private	::	initialised	=	.false.	True if this module has been initialised

Interfaces

public interface init_crfftw

private subroutine init_crfftw_1d(fft, direction, n, howmany, transposed)

Create FFTW plan suitable for 1D complex to real transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	n	Number of points in array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
logical,	intent(in),	optional	::	transposed	If true, then take 42 of transpose of array

private subroutine init_crfftw_2d(fft, direction, m, n, howmany, stride_)

Create FFTW plan suitable for 2D complex to real transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	m	Number of points in first dimension of array to transform
integer,	intent(in)		::	n	Number of points in second dimension of array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
integer,	intent(in),	optional	::	stride_	Stride of array if different from `howmany`

public interface init_rcfftw

private subroutine init_rcfftw_1d(fft, direction, n, howmany, transposed)

Create FFTW plan suitable for 1D real to complex transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	n	Number of points in array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
logical,	intent(in),	optional	::	transposed	If true, then take 42 of transpose of array

private subroutine init_rcfftw_2d(fft, direction, m, n, howmany, stride_)

Create FFTW plan suitable for 2D real to complex transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	m	Number of points in first dimension of array to transform
integer,	intent(in)		::	n	Number of points in second dimension of array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
integer,	intent(in),	optional	::	stride_	Stride of array if different from `howmany`

Derived Types

type, public :: fft_type

Information about a planned 42 transform

Components

Type	Visibility		Name		Initial
logical,	public	::	created	=	.false.	True if the plan has been created
integer,	public	::	n	=	0	Number of points in the array to be transformed
integer,	public	::	direction	=	0	Direction of the 42, can be either FFT_FORWARD or FFTW_BACKWARD
type(C_PTR),	public	::	plan	=	C_NULL_PTR	The FFTW plan object
integer,	public	::	howmany	=	0	How many independent slices in the array to be transformed
logical,	public	::	strided	=	.false.	True if the array is strided or 2D
real,	public	::	scale	=	0	Normalisation factor
logical,	public	::	must_scale	=	.false.	If true, then the result of the 42 needs to be multiplied by scale. If false, then the scaling can be skipped, saving some work

Type-Bound Procedures

procedure , public :: execute_c2r Subroutine
procedure , public :: execute_r2c Subroutine
procedure , public :: execute_c2c Subroutine
procedure , public :: delete => delete_fft Subroutine
procedure , private :: init => basic_init Subroutine

Functions

private pure function fftw_flags()

Set flags for FFTW3

Arguments

None

Return Value integer

Subroutines

private subroutine execute_c2c(self, array_in, array_out)

Small wrapper to bind execute c2c to fft_type

Arguments

Type	Intent	Attributes		Name
class(fft_type),	intent(in)		::	self
complex,	intent(inout),	dimension(*)	::	array_in
complex,	intent(out),	dimension(*)	::	array_out

private subroutine execute_r2c(self, array_in, array_out)

Small wrapper to bind execute r2c to fft_type

Arguments

Type	Intent	Attributes		Name
class(fft_type),	intent(in)		::	self
real,	intent(inout),	dimension(*)	::	array_in
complex,	intent(out),	dimension(*)	::	array_out

private subroutine execute_c2r(self, array_in, array_out)

Small wrapper to bind execute c2r to fft_type

Arguments

Type	Intent	Attributes		Name
class(fft_type),	intent(in)		::	self
complex,	intent(inout),	dimension(*)	::	array_in
real,	intent(out),	dimension(*)	::	array_out

private subroutine delete_fft(self)

Destroy 42 plan

Arguments

Type	Intent	Optional	Attributes		Name
class(fft_type),	intent(inout)			::	self

private subroutine init_fft_work()

Perform any one off setup of the fft library. This is currently mostly only needed for builds with OpenMP for threaded transforms.

Arguments

None

private subroutine basic_init(self, n, direction, howmany, strided)

Does some common initialisation for fft_type

Arguments

Type	Intent		Name
class(fft_type),	intent(inout)	::	self
integer,	intent(in)	::	n	Number of points
integer,	intent(in)	::	direction	Direction of 42, must be either FFT_TO_REAL_SPACE or FFT_TO_SPECTRAL_SPACE
integer,	intent(in)	::	howmany	Number of independent FFTs
logical,	intent(in)	::	strided	Is array strided/2D

public subroutine init_z(fft, direction, n, howmany)

FIXME : Add documentation

Arguments

Type	Intent		Name
type(fft_type),	intent(out)	::	fft
integer,	intent(in)	::	direction
integer,	intent(in)	::	n
integer,	intent(in)	::	howmany

public subroutine init_ccfftw(fft, direction, n, howmany, data_array, transpose, m)

Create an FFTW plan for complex-to-complex transforms

Arguments

Type	Intent	Optional	Attributes		Name
type(fft_type),	intent(out)			::	fft	The created plan
integer,	intent(in)			::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)			::	n	Number of points in array to transform
integer,	intent(in)			::	howmany	Number of independent FFTs in array
complex,	intent(inout),		dimension(:,:)	::	data_array	Example array to transform
logical,	intent(in),	optional		::	transpose	If true, then take 42 of transpose of array
integer,	intent(in),	optional		::	m	Size of transpose direction. Required if `transpose` is true

private subroutine init_rcfftw_1d(fft, direction, n, howmany, transposed)

Create FFTW plan suitable for 1D real to complex transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	n	Number of points in array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
logical,	intent(in),	optional	::	transposed	If true, then take 42 of transpose of array

private subroutine init_crfftw_1d(fft, direction, n, howmany, transposed)

Create FFTW plan suitable for 1D complex to real transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	n	Number of points in array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
logical,	intent(in),	optional	::	transposed	If true, then take 42 of transpose of array

private subroutine init_rcfftw_2d(fft, direction, m, n, howmany, stride_)

Create FFTW plan suitable for 2D real to complex transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	m	Number of points in first dimension of array to transform
integer,	intent(in)		::	n	Number of points in second dimension of array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
integer,	intent(in),	optional	::	stride_	Stride of array if different from `howmany`

private subroutine init_crfftw_2d(fft, direction, m, n, howmany, stride_)

Create FFTW plan suitable for 2D complex to real transformation

Arguments

Type	Intent	Optional		Name
type(fft_type),	intent(out)		::	fft	The created plan
integer,	intent(in)		::	direction	Direction of the transformation, either FFT_TO_SPECTRAL_SPACE or FFT_TO_REAL_SPACE
integer,	intent(in)		::	m	Number of points in first dimension of array to transform
integer,	intent(in)		::	n	Number of points in second dimension of array to transform
integer,	intent(in)		::	howmany	Number of independent FFTs in array
integer,	intent(in),	optional	::	stride_	Stride of array if different from `howmany`

public subroutine finish_fft_work()

Restore FFTW to pristine state

Arguments

None

public subroutine save_wisdom(filename)

Save FFTW wisdom to file

Arguments

Type	Intent	Optional	Attributes		Name
character(len=*),	intent(in)			::	filename

public subroutine load_wisdom(filename)

Load FFTW wisdom from file

Arguments

Type	Intent	Optional	Attributes		Name
character(len=*),	intent(in)			::	filename

fft_work Module

Contents

Uses

Contents

Variables

Interfaces

public interface init_crfftw

private subroutine init_crfftw_1d(fft, direction, n, howmany, transposed)

Arguments

private subroutine init_crfftw_2d(fft, direction, m, n, howmany, stride_)

Arguments

public interface init_rcfftw

private subroutine init_rcfftw_1d(fft, direction, n, howmany, transposed)

Arguments

private subroutine init_rcfftw_2d(fft, direction, m, n, howmany, stride_)

Arguments

Derived Types

type, public :: fft_type

Components

Type-Bound Procedures

Functions

private pure function fftw_flags()

Arguments

Return Value integer

Subroutines

private subroutine execute_c2c(self, array_in, array_out)

Arguments

private subroutine execute_r2c(self, array_in, array_out)

Arguments

private subroutine execute_c2r(self, array_in, array_out)

Arguments

private subroutine delete_fft(self)

Arguments

private subroutine init_fft_work()

Arguments

private subroutine basic_init(self, n, direction, howmany, strided)

Arguments

public subroutine init_z(fft, direction, n, howmany)

Arguments

public subroutine init_ccfftw(fft, direction, n, howmany, data_array, transpose, m)

Arguments

private subroutine init_rcfftw_1d(fft, direction, n, howmany, transposed)

Arguments

private subroutine init_crfftw_1d(fft, direction, n, howmany, transposed)

Arguments

private subroutine init_rcfftw_2d(fft, direction, m, n, howmany, stride_)

Arguments

private subroutine init_crfftw_2d(fft, direction, m, n, howmany, stride_)

Arguments

public subroutine finish_fft_work()

Arguments

public subroutine save_wisdom(filename)

Arguments

public subroutine load_wisdom(filename)

Arguments