fftw-wisdom - create wisdom (pre-optimized FFTs)
fftw-wisdom [OPTION]... [SIZE]...
fftw-wisdom is a utility to generate FFTW wisdom files, which 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:
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
/etc/fftw/wisdom 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 option) and
the output wisdom file can then be copied (as root) to /etc/fftw/ or
The fftw-wisdom 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 fftw-
wisdom reads this existing wisdom (unless the -n option is 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 option).
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:
<type> is either ´c´ (complex), ´r´ (real, r2c/c2r), or ´k´ (r2r, per-
dimension kinds, specified in the geometry, below).
<inplace> is either ´i´ (in place) or ´o´ (out of place).
<direction> 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
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).
Display help on the command-line options and usage.
Print the version number and copyright information.
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.
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. 16x16x16).
-t hours, --time-limit=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, --output-file=file
Send wisdom output to file rather than to standard output (the
-m, --measure; -e, --estimate; -x, --exhaustive
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 --exhaustive mode).
Do not import the system wisdom from /etc/fftw/wisdom (which is
normally read by default).
-w file, --wisdom-file=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
Send bug reports to email@example.com.
Written by Steven G. Johnson and Matteo Frigo.
Copyright (c) 2003, 2007-8 Matteo Frigo
Copyright (c) 2003, 2007-8 Massachusetts Institute of Technology