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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<html>
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<head><title>
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FFTW Frequently Asked Questions with Answers
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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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<META name="description"
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      content="Frequently asked questions and answers (FAQ) for FFTW.">
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<link rel="Bookmark" title="FFTW FAQ" href="index.html">
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<LINK rel="Bookmark" title="FFTW Home Page"
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      href="http://theory.lcs.mit.edu/~fftw">
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<LINK rel="Bookmark" title="FFTW Manual"
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</head><body text="#000000" bgcolor="#FFFFFF"><h1>
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FFTW Frequently Asked Questions with Answers
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</h1>
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This is the list of Frequently Asked Questions about FFTW, a
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collection of fast C routines for computing the Discrete Fourier
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Transform in one or more dimensions.  
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<h1>
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Index
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</h1>
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<ul>
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<li><b><font size="+2"><a href="section1.html" rel=subdocument>Section 1.  Introduction and General Information</a></font></b>
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<li><a href="section1.html#whatisfftw" rel=subdocument>Q1.1. What is FFTW?</a>
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<li><a href="section1.html#whereisfftw" rel=subdocument>Q1.2. How do I obtain FFTW?</a>
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<li><a href="section1.html#isfftwfree" rel=subdocument>Q1.3. Is FFTW free software?</a>
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<li><a href="section1.html#nonfree" rel=subdocument>Q1.4. What is this about non-free licenses?</a>
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<br><br><li><b><font size="+2"><a href="section2.html" rel=subdocument>Section 2.  Installing FFTW</a></font></b>
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<li><a href="section2.html#systems" rel=subdocument>Q2.1. Which systems does FFTW run on?</a>
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<li><a href="section2.html#runOnDOS" rel=subdocument>Q2.2. Does FFTW run on DOS/Windows?</a>
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<li><a href="section2.html#compilerCrashes" rel=subdocument>Q2.3. My compiler crashes when compiling FFTW.</a>
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<li><a href="section2.html#solarisSucks" rel=subdocument>Q2.4. FFTW does not compile on Solaris, complaining about
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<code>const</code>.</a>
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<li><a href="section2.html#languages" rel=subdocument>Q2.5. Which language is FFTW written in?</a>
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<li><a href="section2.html#fortran" rel=subdocument>Q2.6. Can I call FFTW from FORTRAN?</a>
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<li><a href="section2.html#cplusplus" rel=subdocument>Q2.7. Can I call FFTW from C++?</a>
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<li><a href="section2.html#whynotfortran" rel=subdocument>Q2.8. Why isn't FFTW written in FORTRAN/C++?</a>
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<li><a href="section2.html#singleprec" rel=subdocument>Q2.9. How do I compile FFTW to run in single precision?</a>
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<br><br><li><b><font size="+2"><a href="section3.html" rel=subdocument>Section 3.  Using FFTW</a></font></b>
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<li><a href="section3.html#slow" rel=subdocument>Q3.1. FFTW seems really slow.</a>
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<li><a href="section3.html#conventions" rel=subdocument>Q3.2. FFTW gives results different from my old
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FFT.</a>
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<li><a href="section3.html#savePlans" rel=subdocument>Q3.3. Can I save FFTW's plans?</a>
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<li><a href="section3.html#whyscaled" rel=subdocument>Q3.4. Why does your inverse transform return a scaled
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result?</a>
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<li><a href="section3.html#centerorigin" rel=subdocument>Q3.5. How can I make FFTW put the origin (zero frequency) at the center of
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its output?</a>
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<li><a href="section3.html#imageaudio" rel=subdocument>Q3.6. How do I FFT an image/audio file in <i>foobar</i> format?</a>
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<li><a href="section3.html#linkfails" rel=subdocument>Q3.7. My program does not link (on Unix).</a>
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<br><br><li><b><font size="+2"><a href="section4.html" rel=subdocument>Section 4.  Internals of FFTW</a></font></b>
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<li><a href="section4.html#howworks" rel=subdocument>Q4.1. How does FFTW work?</a>
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<li><a href="section4.html#whyfast" rel=subdocument>Q4.2. Why is FFTW so fast?</a>
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<li><a href="section4.html#wisdom" rel=subdocument>Q4.3. What is this <code>wisdom</code> thing?</a>
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<li><a href="section4.html#whywisdom" rel=subdocument>Q4.4. Why do you use <code>wisdom</code>? I just wanted to save a plan.</a>
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<br><br><li><b><font size="+2"><a href="section5.html" rel=subdocument>Section 5.  Known bugs</a></font></b>
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<li><a href="section5.html#rfftwndbug" rel=subdocument>Q5.1. FFTW 1.1 crashes in rfftwnd on Linux.</a>
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<li><a href="section5.html#fftwmpibug" rel=subdocument>Q5.2. The MPI transforms in FFTW 1.2 give incorrect results/leak
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memory.</a>
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<li><a href="section5.html#testsingbug" rel=subdocument>Q5.3. The test programs in FFTW 1.2.1 fail when I change FFTW to use single
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precision.</a>
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<li><a href="section5.html#teststoobig" rel=subdocument>Q5.4. The test program in FFTW 1.2.1 fails for n &gt;
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46340.</a>
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<li><a href="section5.html#linuxthreads" rel=subdocument>Q5.5. The threaded code fails on Linux Redhat 5.0</a>
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<li><a href="section5.html#bigrfftwnd" rel=subdocument>Q5.6. FFTW 2.0's rfftwnd fails for rank &gt; 1 transforms with a final
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dimension &gt;= 65536.</a>
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<li><a href="section5.html#primebug" rel=subdocument>Q5.7. FFTW 2.0's complex transforms give the wrong results with prime
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factors 17 to 97.</a>
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<li><a href="section5.html#mpichbug" rel=subdocument>Q5.8. FFTW 2.1.1's MPI test programs crash with
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MPICH.</a>
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</ul><hr>
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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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