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85 lines
3.6 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<head><title>
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FFTW FAQ - Section 1
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</title>
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<link rev="made" href="mailto:fftw@fftw.org">
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<link rel="Contents" href="index.html">
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<link rel="Start" href="index.html">
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<link rel="Next" href="section2.html"><link rel="Bookmark" title="FFTW FAQ" href="index.html">
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</head><body text="#000000" bgcolor="#FFFFFF"><h1>
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FFTW FAQ - Section 1 <br>
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Introduction and General Information
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</h1>
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<ul>
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<li><a href="#whatisfftw" rel=subdocument>Q1.1. What is FFTW?</a>
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<li><a href="#whereisfftw" rel=subdocument>Q1.2. How do I obtain FFTW?</a>
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<li><a href="#isfftwfree" rel=subdocument>Q1.3. Is FFTW free software?</a>
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<li><a href="#nonfree" rel=subdocument>Q1.4. What is this about non-free licenses?</a>
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<li><a href="#west" rel=subdocument>Q1.5. In the West? I thought MIT was in the East?</a>
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</ul><hr>
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<h2><A name="whatisfftw">
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Question 1.1. What is FFTW?
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</A></h2>
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FFTW is a free collection of fast C routines for computing the
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Discrete Fourier Transform in one or more dimensions. It includes
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complex, real, symmetric, and parallel transforms, and can handle
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arbitrary array sizes efficiently. FFTW is typically faster than
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other publically-available FFT implementations, and is even
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competitive with vendor-tuned libraries. (See our web page for
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extensive benchmarks.) To achieve this performance, FFTW uses novel
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code-generation and runtime self-optimization techniques (along with
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many other tricks).
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<h2><A name="whereisfftw">
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Question 1.2. How do I obtain FFTW?
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</A></h2>
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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>.
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<h2><A name="isfftwfree">
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Question 1.3. Is FFTW free software?
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</A></h2>
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Starting with version 1.3, FFTW is Free Software in the technical
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sense defined by the Free Software Foundation (see
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<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 were
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distributed without fee for noncommercial use, but were not
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technically ``free.''
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<p>
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Non-free licenses for FFTW are also available that permit different
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terms of use than the GPL.
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<h2><A name="nonfree">
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Question 1.4. What is this about non-free
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licenses?
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</A></h2>
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The non-free licenses are for companies that wish to use FFTW in their
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products but are unwilling to release their software under the GPL
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(which would require them to release source code and allow free
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redistribution). Such users can purchase an unlimited-use license
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from MIT. Contact us for more details.
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<p>
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We could instead have released FFTW under the LGPL, or even disallowed
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non-Free usage. Suffice it to say, however, that MIT owns the
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copyright to FFTW and they only let us GPL it because we convinced
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them that it would neither affect their licensing revenue nor irritate
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existing licensees.
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<h2><A name="west">
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Question 1.5. In the West? I thought MIT was in the
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East?
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</A></h2>
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Not to an Italian. You could say that we're a Spaghetti Western
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(with apologies to Sergio Leone). <hr>
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Next: <a href="section2.html" rel=precedes>Installing FFTW</a>.<br>
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<a href="index.html" rev=subdocument>Return to contents</a>.<p>
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<address>
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<A href="http://www.fftw.org">Matteo Frigo and Steven G. Johnson</A> / <A href="mailto:fftw@fftw.org">fftw@fftw.org</A>
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- 14 September 2021
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</address><br>
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Extracted from FFTW Frequently Asked Questions with Answers,
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Copyright © 2021 Matteo Frigo and Massachusetts Institute of Technology.
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</body></html>
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