FFTW FAQ - Section 1
Introduction and General Information


Question 1.1. What is FFTW ?

FFTW is a collection of fast C routines for computing the Discrete Fourier Transform in one or more dimensions. FFTW is unique in two respects. First, it is not just optimized for arrays whose sizes are powers of 2, 3, or other small numbers. Instead, FFTW comes with a code generator that produces C programs for any particular array size you may care about. Second, it doesn't use a fixed strategy for performing the transform. There are usually many ways to decompose a big problem into small problems, and the optimal way often depends on many unpredictable factors. Unlike other programs, FFTW can find the optimal decomposition at runtime for the machine it is running on.

Question 1.2. How do I obtain FFTW?

FFTW can be found at the FFTW web page. You can also retrieve it from theory.lcs.mit.edu in /pub/fftw.

As of the present date, the latest version is 1.3.

Question 1.3. Is FFTW free software?

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

Nonfree versions of FFTW are still available under terms that, unlike the General Public License, do not require you to accompany any object code using FFTW with the corresponding source code. For these different terms, you must purchase a license from MIT's Technology Licensing Office. Users interested in such a license should contact the authors.


Next: Installing FFTW.
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Matteo Frigo and Steven G. Johnson / fftw@theory.lcs.mit.edu - 10 April 1998

Extracted from FFTW Frequently Asked Questions with Answers, Copyright © 1998 Massachusetts Institute of Technology.