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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><html><head><title>FFTW FAQ - Section 1</title><link rev="made" href="mailto:fftw@fftw.org"><link rel="Contents" href="index.html"><link rel="Start" href="index.html"><link rel="Next" href="section2.html"><link rel="Bookmark" title="FFTW FAQ" href="index.html"></head><body text="#000000" bgcolor="#FFFFFF"><h1>FFTW FAQ - Section 1 <br>Introduction and General Information</h1><ul><li><a href="#whatisfftw" rel=subdocument>Q1.1. What is FFTW?</a><li><a href="#whereisfftw" rel=subdocument>Q1.2. How do I obtain FFTW?</a><li><a href="#isfftwfree" rel=subdocument>Q1.3. Is FFTW free software?</a><li><a href="#nonfree" rel=subdocument>Q1.4. What is this about non-free licenses?</a></ul><hr><h2><A name="whatisfftw">Question 1.1. What is FFTW?</A></h2>FFTW is a free collection of fast C routines for computing theDiscrete Fourier Transform in one or more dimensions. It includescomplex, real, and parallel transforms, and can handle arbitrary arraysizes efficiently. FFTW is typically faster than otherpublically-available FFT implementations, and is even competitive withvendor-tuned libraries. (See our web page for extensive benchmarks.)To achieve this performance, FFTW uses novel code-generation andruntime self-optimization techniques (along with many other tricks). <h2><A name="whereisfftw">Question 1.2. How do I obtain FFTW?</A></h2>FFTW can be found at <A href="http://www.fftw.org">the FFTW web page</A>. You can also retrieve it from <code>ftp.fftw.org</code> in <A href="ftp://ftp.fftw.org/pub/fftw"><code>/pub/fftw</code></A>. <h2><A name="isfftwfree">Question 1.3. Is FFTW free software?</A></h2>Starting with version 1.3, FFTW is Free Software in the technicalsense defined by the Free Software Foundation (see<A href="http://www.gnu.org/philosophy/categories.html">Categories of Free and Non-Free Software</A>), and is distributed under the terms of the GNU General Public License. Previous versions of FFTW weredistributed without fee for noncommercial use, but were nottechnically ``free.'' <p>Non-free licenses for FFTW are also available that permit differentterms of use than the GPL. <h2><A name="nonfree">Question 1.4. What is this about non-freelicenses?</A></h2>The non-free licenses are for companies that wish to use FFTW in theirproducts but are unwilling to release their software under the GPL(which would require them to release source code and allow freeredistribution). Such users can purchase an unlimited-use licensefrom MIT. Contact us for more details. <p>We could instead have released FFTW under the LGPL, or even disallowednon-Free usage. Suffice it to say, however, that MIT owns thecopyright to FFTW and they only let us GPL it because we convincedthem that it would neither affect their licensing revenue nor irritateexisting licensees. <hr>Next: <a href="section2.html" rel=precedes>Installing FFTW</a>.<br><a href="index.html" rev=subdocument>Return to contents</a>.<p><address><A href="http://www.fftw.org">Matteo Frigo and Steven G. Johnson</A> / <A href="mailto:fftw@fftw.org">fftw@fftw.org</A>- 24 March 2003</address><br>Extracted from FFTW Frequently Asked Questions with Answers,Copyright © 2003 Massachusetts Institute of Technology.</body></html>⌨️ 快捷键说明
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