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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@theory.lcs.mit.edu">
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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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</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, and parallel transforms, and can handle arbitrary array
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sizes efficiently.  FFTW is typically faster than other
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publically-available FFT implementations, and is even competitive with
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vendor-tuned libraries.  (See our web page for extensive benchmarks.)
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To achieve this performance, FFTW uses novel code-generation and
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runtime self-optimization techniques (along with 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://theory.lcs.mit.edu/~fftw/">the FFTW web page</A>.  You can also retrieve it from <code>theory.lcs.mit.edu</code> in <A href="ftp://theory.lcs.mit.edu/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.  <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://theory.lcs.mit.edu/~fftw/">Matteo Frigo and Steven G. Johnson</A> / <A href="mailto:fftw@theory.lcs.mit.edu">fftw@theory.lcs.mit.edu</A>
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- 18 May 1999
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</address><br>
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Extracted from FFTW Frequently Asked Questions with Answers,
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Copyright &copy; 1999 Massachusetts Institute of Technology.
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