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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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2 <html>
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3 <head><title>
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4 FFTW FAQ - Section 1
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5 </title>
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6 <link rev="made" href="mailto:fftw@fftw.org">
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7 <link rel="Contents" href="index.html">
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8 <link rel="Start" href="index.html">
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9 <link rel="Next" href="section2.html"><link rel="Bookmark" title="FFTW FAQ" href="index.html">
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10 </head><body text="#000000" bgcolor="#FFFFFF"><h1>
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11 FFTW FAQ - Section 1 <br>
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12 Introduction and General Information
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13 </h1>
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14
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15 <ul>
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16 <li><a href="#whatisfftw" rel=subdocument>Q1.1. What is FFTW?</a>
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17 <li><a href="#whereisfftw" rel=subdocument>Q1.2. How do I obtain FFTW?</a>
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18 <li><a href="#isfftwfree" rel=subdocument>Q1.3. Is FFTW free software?</a>
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19 <li><a href="#nonfree" rel=subdocument>Q1.4. What is this about non-free licenses?</a>
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20 <li><a href="#west" rel=subdocument>Q1.5. In the West? I thought MIT was in the East?</a>
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21 </ul><hr>
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22
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23 <h2><A name="whatisfftw">
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24 Question 1.1. What is FFTW?
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25 </A></h2>
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26
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27 FFTW is a free collection of fast C routines for computing the
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28 Discrete Fourier Transform in one or more dimensions. It includes
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29 complex, real, symmetric, and parallel transforms, and can handle
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30 arbitrary array sizes efficiently. FFTW is typically faster than
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31 other publically-available FFT implementations, and is even
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32 competitive with vendor-tuned libraries. (See our web page for
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33 extensive benchmarks.) To achieve this performance, FFTW uses novel
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34 code-generation and runtime self-optimization techniques (along with
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35 many other tricks).
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36 <h2><A name="whereisfftw">
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37 Question 1.2. How do I obtain FFTW?
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38 </A></h2>
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39
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40 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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41 <h2><A name="isfftwfree">
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42 Question 1.3. Is FFTW free software?
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43 </A></h2>
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44
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45 Starting with version 1.3, FFTW is Free Software in the technical
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46 sense defined by the Free Software Foundation (see
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47 <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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48 distributed without fee for noncommercial use, but were not
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49 technically ``free.''
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50 <p>
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51 Non-free licenses for FFTW are also available that permit different
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52 terms of use than the GPL.
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53 <h2><A name="nonfree">
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54 Question 1.4. What is this about non-free
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55 licenses?
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56 </A></h2>
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57
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58 The non-free licenses are for companies that wish to use FFTW in their
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59 products but are unwilling to release their software under the GPL
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60 (which would require them to release source code and allow free
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61 redistribution). Such users can purchase an unlimited-use license
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62 from MIT. Contact us for more details.
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63
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64 <p>
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65 We could instead have released FFTW under the LGPL, or even disallowed
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66 non-Free usage. Suffice it to say, however, that MIT owns the
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67 copyright to FFTW and they only let us GPL it because we convinced
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68 them that it would neither affect their licensing revenue nor irritate
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69 existing licensees.
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70 <h2><A name="west">
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71 Question 1.5. In the West? I thought MIT was in the
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72 East?
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73 </A></h2>
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74
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75 Not to an Italian. You could say that we're a Spaghetti Western
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76 (with apologies to Sergio Leone). <hr>
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77 Next: <a href="section2.html" rel=precedes>Installing FFTW</a>.<br>
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78 <a href="index.html" rev=subdocument>Return to contents</a>.<p>
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79 <address>
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80 <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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81 - 30 July 2016
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82 </address><br>
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83 Extracted from FFTW Frequently Asked Questions with Answers,
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84 Copyright © 2016 Matteo Frigo and Massachusetts Institute of Technology.
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85 </body></html>
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