fftw-wisdom - create wisdom (pre-optimized FFTs)
is a utility to generate FFTW wisdom
contain saved information about how to optimally compute (Fourier) transforms
of various sizes. FFTW is a free library to compute discrete Fourier
transforms in one or more dimensions, for arbitrary sizes, and of both real
and complex data, among other related operations. More information on FFTW can
be found at the FFTW home page: http://www.fftw.org
Programs using FFTW can be written to load wisdom from an arbitrary file,
string, or other source. Moreover, it is likely that many FFTW-using programs
will load the system wisdom
file, which is stored in
by default. fftw-wisdom
can be used to create
or add to such wisdom files. In its most typical usage, the wisdom file can be
created to pre-plan a canonical set of sizes (see below) via:
fftw-wisdom -v -c -o wisdom
(this will take many hours, which can be limited by the -t
the output wisdom
file can then be copied (as root) to
program normally writes the wisdom directly to standard
output, but this can be changed via the -o
option, as in the example
If the system wisdom file /etc/fftw/wisdom
already exists, then
reads this existing wisdom (unless the -n
specified) and outputs both the old wisdom and any newly created wisdom. In
this way, it can be used to add new transform sizes to the existing system
wisdom (or other wisdom file, with the -w
Although a canonical set of sizes to optimize is specified by the -c
option, the user can also specify zero or more non-canonical transform sizes
and types to optimize, via the SIZE
arguments following the option
flags. Alternatively, the sizes to optimize can be read from standard input
(whitespace-separated), if a SIZE
argument of "-" is
Sizes are specified by the syntax:
> is either ´c´ (complex), ´r´
(real, r2c/c2r), or ´k´ (r2r, per-dimension kinds, specified in
the geometry, below).
> is either ´i´ (in place) or
´o´ (out of place).
> is either ´f´ (forward) or
´b´ (backward). The < direction
> should be omitted
for ´k´ transforms, where it is specified via the geometry
> is the size and dimensionality of the transform, where
different dimensions are separated by ´x´ (e.g.
´16x32´ for a two-dimensional 16 by 32 transform). In the case
of ´k´ transforms, the size of each dimension is followed by a
"type" string, which can be one of
f/b/h/e00/e01/e10/e11/o00/o01/o10/o11 for R2HC/HC2R/DHT/REDFT00/.../RODFT11,
respectively, as defined in the FFTW manual.
For example, ´cif12x13x14´ is a three-dimensional 12 by 13 x 14
complex DFT operating in-place. ´rob65536´ is a one-dimensional
size-65536 out-of-place complex-to-real (backwards) transform operating on
Hermitian-symmetry input. ´ki10hx20e01´ is a two-dimensional 10
by 20 r2r transform where the first dimension is a DHT and the second
dimension is an REDFT01 (DCT-III).
- -h, --help
- Display help on the command-line options and usage.
- -V, --version
- Print the version number and copyright information.
- -v, --verbose
- Verbose output. (You can specify this multiple times, or
supply a numeric argument greater than 1, to increase the verbosity
level.) Note that the verbose output will be mixed with the wisdom output
(making it impossible to import), unless you write the wisdom to a file
via the -o option.
- -c, --canonical
- Optimize/pre-plan a canonical set of sizes: all powers of
two and ten up to 2^20 (1048576), including both real and complex, forward
and backwards, in-place and out-of-place transforms. Also includes two-
and three-dimensional transforms of equal-size dimensions (e.g.
- -t hours,
- Stop after a time of hours (hours) has elapsed,
outputting accumulated wisdom. (The problems are planned in increasing
order of size.) Defaults to 0, indicating no time limit.
- -o file,
- Send wisdom output to file rather than to standard
output (the default).
- -m, --measure; -e, --estimate;
- Normally, fftw-wisdom creates plans in FFTW_PATIENT
mode, but with these options you can instead use FFTW_MEASURE,
FFTW_ESTIMATE, or FFTW_EXHAUSTIVE modes, respectively, as described in
more detail by the FFTW manual.
Note that wisdom is tagged with the planning patience level, and a single
file can mix different levels of wisdom (e.g. you can mostly use the
patient default, but plan a few sizes that you especially care about in
- -n, --no-system-wisdom
- Do not import the system wisdom from
/etc/fftw/wisdom (which is normally read by default).
- -w file,
- Import wisdom from file (in addition to the system
wisdom, unless -n is specified). Multiple wisdom files can be read
via multiple -w options. If file is "-", then read
wisdom from standard input.
- -T N, --threads=N
- Plan with N threads. This option is only present if
FFTW was configured with thread support.
Send bug reports to email@example.com.
Written by Steven G. Johnson and Matteo Frigo.
Copyright (c) 2003, 2007-14 Matteo Frigo
Copyright (c) 2003, 2007-14 Massachusetts Institute of Technology