FFTW(3) User Contributed Perl Documentation FFTW(3)NAMEPDL::FFTW - PDL interface to the Fastest Fourier Transform in the West
v2.x
DESCRIPTION
This is a means to interface PDL with the FFTW library. It's similar to
the standard FFT routine but it's usually faster and has support for
real transforms. It works well for the types of PDLs for which was the
library was compiled (otherwise it must do conversions).
SYNOPSIS
use PDL::FFTW
load_wisdom("file_name");
out_cplx_pdl = fftw(in_cplx_pdl);
out_cplx_pdl = ifftw(in_cplx_pdl);
out_cplx_pdl = rfftw(in_real_pdl);
out_real_pdl = irfftw(in_cplx_pdl);
cplx_pdl = nfftw(cplx_pdl);
cplx_pdl = infftw(cplx_pdl);
cplx_pdl = Cmul(a_cplx_pdl, b_cplx_pdl);
cplx_pdl = Cconj(a_cplx_pdl);
real_pdl = Cmod(a_cplx_pdl);
real_pdl = Cmod2(a_cplx_pdl);
FFTW documentation
Please refer to the FFTW documentation for a better understanding of
these functions.
Note that complex numbers are represented as piddles with leading
dimension size 2 (real/imaginary pairs).
FUNCTIONS
load_wisdom
Loads the wisdom from a file for better FFTW performance.
The wisdom is automatically saved when the program ends. It will be
automagically called when the variable $PDL::FFT::wisdom is set to a
file name. For example, the following is a useful idiom to have in
your .perldlrc file:
$PDL::FFT::wisdom = "$ENV{HOME}/.fftwisdom"; # save fftw wisdom in this file
Explicit usage:
load_wisdom($fname);
fftw
calculate the complex FFT of a real piddle (complex input, complex
output)
$pdl_cplx = fftw $pdl_cplx;
ifftw
Complex inverse FFT (complex input, complex output).
$pdl_cplx = ifftw $pdl_cplx;
nfftw
Complex inplace FFT (complex input, complex output).
$pdl_cplx = nfftw $pdl_cplx;
infftw
Complex inplace inverse FFT (complex input, complex output).
$pdl_cplx = infftw $pdl_cplx;
rfftw
Real FFT. For an input piddle of dimensions [n1,n2,...] the output is
[2,(n1/2)+1,n2,...] (real input, complex output).
$pdl_cplx = fftw $pdl_real;
irfftw
Real inverse FFT. Have a look at rfftw to understand the format. USE
ONLY an even n1! (complex input, real output)
$pdl_real = ifftw $pdl_cplx;
nrfftw
Real inplace FFT. If you want a transformation on a piddle with
dimensions [n1,n2,....] you MUST pass in a piddle with dimensions
[2*(n1/2+1),n2,...] (real input, complex output).
Use with care due to dimension restrictions mentioned below. For
details check the html docs that come with the fftw library.
$pdl_cplx = nrfftw $pdl_real;
inrfftw
Real inplace inverse FFT. Have a look at nrfftw to understand the
format. USE ONLY an even first dimension size! (complex input, real
output)
$pdl_real = infftw $pdl_cplx;
rfftwconv
ND convolution using real ffts from the FFTW library
$conv = rfftwconv $im, kernctr $im, $k; # kernctr is from PDL::FFT
fftwconv
ND convolution using complex ffts from the FFTW library
Assumes real input!
$conv = fftwconv $im, kernctr $im, $k; # kernctr is from PDL::FFT
Cmul
Signature: (a(n); b(n); [o]c(n))
Complex multiplication
$out_pdl_cplx = Cmul($a_pdl_cplx,$b_pdl_cplx);
Cscale
Signature: (a(n); b(); [o]c(n))
Complex by real multiplation.
Cscale($a_pdl_cplx,$b_pdl_real);
Cdiv
Signature: (a(n); b(n); [o]c(n))
Complex division.
$out_pdl_cplx = Cdiv($a_pdl_cplx,$b_pdl_cplx);
Cbmul
Signature: (a(n); b(n))
Complex inplace multiplication.
Cbmul($a_pdl_cplx,$b_pdl_cplx);
Cbscale
Signature: (a(n); b())
Complex inplace multiplaction by real.
Cbscale($a_pdl_cplx,$b_pdl_real);
Cconj
Signature: (a(n); [o]c(n))
Complex conjugate.
$out_pdl_cplx = Cconj($a_pdl_cplx);
Cbconj
Signature: (a(n))
Complex inplace conjugate.
Cbconj($a_pdl_cplx);
Cexp
Signature: (a(n); [o]c(n))
Complex exponentation.
$out_pdl_cplx = Cexp($a_pdl_cplx);
Cbexp
Signature: (a(n))
Complex inplace exponentation.
$out_pdl_cplx = Cexp($a_pdl_cplx);
Cmod
Signature: (a(n); [o]c())
modulus of a complex piddle.
$out_pdl_real = Cmod($a_pdl_cplx);
Carg
Signature: (a(n); [o]c())
argument of a complex number.
$out_pdl_real = Carg($a_pdl_cplx);
Cmod2
Signature: (a(n); [o]c())
Returns squared modulus of a complex number.
$out_pdl_real = Cmod2($a_pdl_cplx);
AUTHOR
Copyright (C) 1999 Christian Pellegrin, 2000 Christian Soeller. All
rights reserved. There is no warranty. You are allowed to redistribute
this software / documentation under certain conditions. For details,
see the file COPYING in the PDL distribution. If this file is separated
from the PDL distribution, the copyright notice should be included in
the file.
perl v5.10.0 2008-08-29 FFTW(3)
