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Math::FFT::Libfftw3 cpan:FRITH last updated on 2018-12-05



Math::FFT::Libfftw3 - An interface to libfftw3.

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use v6;

use Math::FFT::Libfftw3::C2C;
use Math::FFT::Libfftw3::Constants; # needed for the FFTW_BACKWARD constant

my @in = (0, π/100 … 2*π)».sin;
put @in».Complex».round(10⁻¹²); # print the original array as complex values rounded to 10⁻¹²
my Math::FFT::Libfftw3::C2C $fft .= new: data => @in;
my @out = $fft.execute;
put @out; # print the direct transform output
my Math::FFT::Libfftw3::C2C $fftr .= new: data => @out, direction => FFTW_BACKWARD;
my @outr = $fftr.execute;
put @outr».round(10⁻¹²); # print the backward transform output rounded to 10⁻¹²
use v6;

use Math::FFT::Libfftw3::C2C;
use Math::FFT::Libfftw3::Constants; # needed for the FFTW_BACKWARD constant

# direct 2D transform
my Math::FFT::Libfftw3::C2C $fft .= new: data => 1..18, dims => (6, 3);
my @out = $fft.execute;
put @out;
# reverse 2D transform
my Math::FFT::Libfftw3::C2C $fftr .= new: data => @out, dims => (6,3), direction => FFTW_BACKWARD;
my @outr = $fftr.execute;
put @outr».round(10⁻¹²);

For more examples see the example directory.


Math::FFT::Libfftw3 provides an interface to libfftw3 and allows you to perform Fast Fourier Transforms.


Math::FFT::Libfftw3::C2C Complex-to-Complex transform

new(:@data!, :@dims?, Int :$direction? = FFTW_FORWARD, Int :$flag? = FFTW_ESTIMATE)

new(:$data!, Int :$direction? = FFTW_FORWARD, Int :$flag? = FFTW_ESTIMATE)

The first constructor accepts any Positional of type Int, Rat, Num, Complex (and IntStr, RatStr, NumStr, ComplexStr); it allows List of Ints, Array of Complex, Seq of Rat, shaped arrays of any base type, etc.

The only mandatory argument is @data. Multidimensional data are expressed in row-major order (see the C Library Documentation) and the array @dims must be passed to the constructor, or the data will be interpreted as a 1D array. If one uses a shaped array, there's no need to pass the @dims array, because the dimensions will be read from the array itself.

The $direction parameter is used to specify a direct or backward transform; it defaults to FFTW_FORWARD.

The $flag parameter specifies the way the underlying library has to analyze the data in order to create a plan for the transform; it defaults to FFTW_ESTIMATE (see the C Library Documentation).

The second constructor accepts a scalar: an object of type Math::Matrix (if that module is installed, otherwise it returns a Failure), a $direction, and a $flag; the meaning of the last two parameters is the same as in the other constructor.

execute(Int :$output? = OUT-COMPLEX --> Positional)

Executes the transform and returns the output array of values as a normalized row-major array. The parameter $output can be optionally used to specify how the array is to be returned:

The default (OUT-COMPLEX) is to return an array of Complex. OUT-REIM makes the execute method return the native representation of the data: an array of couples of real/imaginary values. OUT-NUM makes the execute method return just the real part of the complex values.

in(Int :$output? = OUT-COMPLEX --> Positional)

Returns the input array, same options as per the output array.


Some of this class' attributes are readable:

Wisdom interface

This interface allows to save and load a plan associated to a transform (There are some caveats. See C Library Documentation).

plan-save(Str $filename --> True)

Saves the plan into a file. Returns True if successful and a Failure object otherwise.

plan-load(Str $filename --> True)

Loads the plan From a file. Returns True if successful and a Failure object otherwise.

Math::FFT::Libfftw3::R2C Real-to-Complex transform

The interface for the R2C transform is slightly different.

In particular:

C Library documentation

For more details on libfftw see the FFTW home. The manual is available here.


This module requires the libfftw3 library to be installed. Please follow the instructions below based on your platform:

Debian Linux

sudo apt-get install libfftw3-double3

The module looks for a library called


To install it using zef (a module management tool):

$ zef update
$ zef install Math::FFT::Libfftw3


To run the tests:

$ prove -e "perl6 -Ilib"


Math::FFT::Libfftw3 relies on a C library which might not be present in one's installation, so it's not a substitute for a pure Perl 6 module. If you need a pure Perl 6 module, Math::FourierTransform works just fine.

This module needs Perl 6 ≥ 2018.09 only if one wants to use shaped arrays as input data. An attempt to feed a shaped array to the new method using $*PERL.compiler.version < v2018.09 results in an exception.


A lot.

The underlying C library provides functions for trasnforming a complex input into a complex output: a c2c transform. There are other possibilities: r2c and c2r transforms (implemented), and r2r transforms:


Future development might change the API or might provide different classes for each data type.


Fernando Santagata

The Artistic License 2.0