Chris@19: Chris@19: Chris@19: Chris@19: FFTW FAQ - Section 1 Chris@19: Chris@19: Chris@19: Chris@19: Chris@19: Chris@19:

Chris@19: FFTW FAQ - Section 1
Chris@19: Introduction and General Information Chris@19:

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Chris@19: Question 1.1. What is FFTW? Chris@19:

Chris@19: Chris@19: FFTW is a free collection of fast C routines for computing the Chris@19: Discrete Fourier Transform in one or more dimensions. It includes Chris@19: complex, real, symmetric, and parallel transforms, and can handle Chris@19: arbitrary array sizes efficiently. FFTW is typically faster than Chris@19: other publically-available FFT implementations, and is even Chris@19: competitive with vendor-tuned libraries. (See our web page for Chris@19: extensive benchmarks.) To achieve this performance, FFTW uses novel Chris@19: code-generation and runtime self-optimization techniques (along with Chris@19: many other tricks). Chris@19:

Chris@19: Question 1.2. How do I obtain FFTW? Chris@19:

Chris@19: Chris@19: FFTW can be found at the FFTW web page. You can also retrieve it from ftp.fftw.org in /pub/fftw. Chris@19:

Chris@19: Question 1.3. Is FFTW free software? Chris@19:

Chris@19: Chris@19: Starting with version 1.3, FFTW is Free Software in the technical Chris@19: sense defined by the Free Software Foundation (see Chris@19: Categories of Free and Non-Free Software), and is distributed under the terms of the GNU General Public License. Previous versions of FFTW were Chris@19: distributed without fee for noncommercial use, but were not Chris@19: technically ``free.'' Chris@19:

Chris@19: Non-free licenses for FFTW are also available that permit different Chris@19: terms of use than the GPL. Chris@19:

Chris@19: Question 1.4. What is this about non-free Chris@19: licenses? Chris@19:

Chris@19: Chris@19: The non-free licenses are for companies that wish to use FFTW in their Chris@19: products but are unwilling to release their software under the GPL Chris@19: (which would require them to release source code and allow free Chris@19: redistribution). Such users can purchase an unlimited-use license Chris@19: from MIT. Contact us for more details. Chris@19: Chris@19:

Chris@19: We could instead have released FFTW under the LGPL, or even disallowed Chris@19: non-Free usage. Suffice it to say, however, that MIT owns the Chris@19: copyright to FFTW and they only let us GPL it because we convinced Chris@19: them that it would neither affect their licensing revenue nor irritate Chris@19: existing licensees. Chris@19:

Chris@19: Question 1.5. In the West? I thought MIT was in the Chris@19: East? Chris@19:

Chris@19: Chris@19: Not to an Italian. You could say that we're a Spaghetti Western Chris@19: (with apologies to Sergio Leone).
Chris@19: Next: Installing FFTW.
Chris@19: Return to contents.

Chris@19:

Chris@19: Matteo Frigo and Steven G. Johnson / fftw@fftw.org Chris@19: - 04 March 2014 Chris@19:

Chris@19: Extracted from FFTW Frequently Asked Questions with Answers, Chris@19: Copyright © 2014 Matteo Frigo and Massachusetts Institute of Technology. Chris@19: