FFTW¶
Usage
use FFTW;
Singlethreaded FFT computations via key routines from FFTW (version 3)
This module defines Chapel wrappers for key singlethreaded 64bit
routines from FFTW (http://www.fftw.org), version 3. For
multithreaded routines, refer to the FFTW_MT
module. Over
time, the intention is to expand these modules to support additional
routines, prioritizing based on requests and feedback from users.
To use this module:
 Ensure that FFTW (version 3) is installed on your system. The
current version of the Chapel module only supports double precision
real(64)
transforms. We do support using the FFTW compatible wrappers provided by the Intel Math Kernel Library (MKL) (see below for usage).  Add
use FFTW;
to your Chapel code.  Include the appropriate libraries in your compilation command.
 For a standard FFTW installation, this may be as simple as including
lfftw3
when compiling. You may also need to use theI
andL
flags to specify the locations of the header and library files if these are in nonstandard locations.  Intel MKL : To use the MKL FFTW wrappers, compile with
sisFFTW_MKL
to include thefftw3_mkl.h
header in addition to the usualfftw3.h
header file. You may also need to addI${MKLROOT}/include/fftw
to point the compiler to the location of these header files. Refer to the Intel MKL documentation for the appropriate libraries to include.
 For a standard FFTW installation, this may be as simple as including
As in standard FFTW usage, the flow is to:
 Create plan(s) using the
plan_dft*
routines.  Execute the plan(s) one or more times using
execute
.  Destroy the plan(s) using
destroy_plan
.  Call
cleanup
.
Note that each of the Chapel plan_dft*
routines
support both inplace and outofplace versions of the
transforms, where the former versions use a single array for both
input and output, and the latter use two distinct arrays.
In future versions of this module, we anticipate improving the plan_dft*() interfaces to make better use of Chapel features and move further away from Cisms (like the overloaded role of flags and the use of Cbased types). Such features are expected to take advantage of Chapel's support for default argument values and keywordbased argument passing. We are also thinking about changing the interface for the inplace routines to use array slicing rather than separate arguments for the array and domain.

config param
isFFTW_MKL
= false¶ Set this to true if you are using the Intel MKL FFTW wrappers

config param
noFFTWsizeChecks
= false¶ Controls executiontime array size checks in the FFTW
plan_dft
routines (set to true to disable checks).

type
fftw_plan
¶ An opaque type used to store and reuse FFTW plans across multiple routines.

proc
plan_dft
(input: [?Din] complex(128), output: [?Dout] complex(128), sign: c_int, flags: c_uint): fftw_plan¶ Creates a plan for an outofplace complextocomplex DFT.
Arguments:  input : [] complex(128)  The input array, which can be of any rank
 output : [] complex(128)  The output array, whose size and shape must match the input array's
 sign : c_int 
FFTW_FORWARD
orFFTW_BACKWARD
 flags : c_int  the bitwiseor of any planningrigor or algorithmrestriction flags that should be used in creating the plan (e.g.,
FFTW_MEASURE

FFTW_PRESERVE_INPUT
)
Returns: The
fftw_plan
representing the resulting plan

proc
plan_dft
(arr: [] complex(128), sign: c_int, flags: c_uint): fftw_plan Creates a plan for an inplace complextocomplex DFT.
Arguments:  arr : [] complex(128)  The array to use as the inplace input/output array.
 sign : c_int 
FFTW_FORWARD
orFFTW_BACKWARD
 flags : c_int  the bitwiseor of any planningrigor or algorithmrestriction flags that should be used in creating the plan (e.g.,
FFTW_MEASURE

FFTW_PRESERVE_INPUT
)
Returns: The
fftw_plan
representing the resulting plan

proc
plan_dft_r2c
(input: [?Din] real(64), output: [?Dout] complex(128), flags: c_uint): fftw_plan¶ Create a plan for a realtocomplex, outofplace DFT.
Arguments:  input : [] real(64)  The input array, which can be of any rank
 output : [] complex(128)  The output array, whose size and shape must match the input array's, except for the leading dimension which should be n/2 + 1, where n is the size of the input array's leading dimension. See the FFTW documentation for more information.
 flags : c_int  the bitwiseor of any planningrigor or algorithmrestriction flags that should be used in creating the plan (e.g.,
FFTW_MEASURE

FFTW_PRESERVE_INPUT
)
Returns: The
fftw_plan
representing the resulting plan

proc
plan_dft_r2c
(realDom: domain, arr: [?D] ?t, flags: c_uint): fftw_plan Create a plan for a realtocomplex, inplace DFT.
Arguments:  realDom : domain  Describes the indices of the 'real' view of the array
 arr : [] T where T is of type real(64) or complex(128) 
The array to be used as the inplace input/output array. If passing in an array of real elements, the leading dimension of the array must be padded to store 2(n/2 + 1) elements, where n is the size of the corresponding dimension of realDom. If passing in an array of complex elements, the leading dimension should be (n/2 + 1). See the FFTW documentation for more information.
 flags : c_int  the bitwiseor of any planningrigor or algorithmrestriction flags that should be used in creating the plan (e.g.,
FFTW_MEASURE

FFTW_PRESERVE_INPUT
)
Returns: The
fftw_plan
representing the resulting plan

proc
plan_dft_c2r
(input: [?Din] complex(128), output: [?Dout] real(64), flags: c_uint): fftw_plan¶ Create a plan for a complextoreal, outofplace DFT.
Arguments:  input : [] complex(128) 
The input array, whose size and shape must match the output array's, except for the leading dimension which should be n/2 + 1, where n is the size of the output array's leading dimension. See the FFTW documentation for more information.
 output : [] real(64)  The output array
 flags : c_int  the bitwiseor of any planningrigor or algorithmrestriction flags that should be used in creating the plan (e.g.,
FFTW_MEASURE

FFTW_PRESERVE_INPUT
)
Returns: The
fftw_plan
representing the resulting plan input : [] complex(128) 

proc
plan_dft_c2r
(realDom: domain, arr: [?D] ?t, flags: c_uint): fftw_plan Create a plan for a complextoreal, inplace DFT.
Arguments:  realDom : domain  Describes the indices of the 'real' view of the array
 arr : [] T where T is of type real(64) or complex(128) 
The array to be used as the inplace input/output array. If passing in an array of real elements, the leading dimension of the array must be padded to store 2(n/2 + 1) elements, where n is the size of the corresponding dimension of realDom. If passing in an array of complex elements, the leading dimension should be (n/2 + 1). See the FFTW documentation for more information.
 flags : c_int  the bitwiseor of any planningrigor or algorithmrestriction flags that should be used in creating the plan (e.g.,
FFTW_MEASURE

FFTW_PRESERVE_INPUT
)
Returns: The
fftw_plan
representing the resulting plan

proc
execute
(const plan: fftw_plan)¶ Execute an FFTW plan.
Arguments: plan : fftw_plan  The plan to execute, as computed by a plan_dft*() routine.

proc
destroy_plan
(plan: fftw_plan)¶ Destroy an FFTW plan.
Arguments: plan : fftw_plan  The plan to destroy

proc
cleanup
()¶ Clean up FFTW overall.

const
FFTW_FORWARD
: c_int¶ Request a forward transform (i.e., use a negative exponent in the transform).

const
FFTW_BACKWARD
: c_int¶ Request a backward transform (i.e., use a positive exponent in the transform).

const
FFTW_ESTIMATE
: c_uint¶ Specify that a simple heuristic should be used to pick a plan quickly. This will prevent the input/output arrays from being overwritten during planning.

const
FFTW_MEASURE
: c_uint¶ Specify that FFTW should try and find an optimized plan by computing several FFTs and measuring their execution time. This can consume some time.

const
FFTW_PATIENT
: c_uint¶ Specify that FFTW should expend a greater effort finding an optimized plan.

const
FFTW_EXHAUSTIVE
: c_uint¶ Specify that FFTW should expend an even greater effort finding an optimized plan.

const
FFTW_WISDOM_ONLY
: c_uint¶ This is a special planning mode that is useful for querying whether wisdom is available. When using it, the plan is only created when wisdom is available for the given problem; otherwise a null plan is returned. This can be combined with other flags to create a plan if the wisdom available was created in that mode (e.g.,
FFTW_WISDOM_ONLY

FFTW_PATIENT
). For more details on this flag and the previous four, refer to Section 4.3.2 of the FFTW manual

const
FFTW_DESTROY_INPUT
: c_uint¶ Specify that an outofplace transform is permitted to overwrite its input array with arbitrary data. This permits more efficient algorithms to be used in some cases.

const
FFTW_PRESERVE_INPUT
: c_uint¶ Specify that an outofplace transform cannot change its input array.

const
FFTW_UNALIGNED
: c_uint¶ Specify that the algorithm may not impose any unusual alignment requirements on the input/output arrays. This flag should not be necessary for current Chapel use since the planner will automatically detect such cases. For more details on this flag and the previous two, refer to Section 4.3.2 of the FFTW manual.