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<head><title>
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FFTW FAQ - Section 5
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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="Previous" href="section4.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 5 <br>
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Known bugs
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</h1>
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<ul>
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<li><a href="#rfftwndbug" rel=subdocument>Q5.1. FFTW 1.1 crashes in rfftwnd on Linux.</a>
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<li><a href="#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="#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="#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="#linuxthreads" rel=subdocument>Q5.5. The threaded code fails on Linux Redhat 5.0</a>
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<li><a href="#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="#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="#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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<h2><A name="rfftwndbug">
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Question 5.1.  FFTW 1.1 crashes in rfftwnd on
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Linux.
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</A></h2>
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This bug was fixed in FFTW 1.2.  There was a bug in
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<code>rfftwnd</code> causing an incorrect amount of memory to be allocated.  The bug showed
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up in Linux with libc-5.3.12 (and nowhere else that we know of).
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<h2><A name="fftwmpibug">
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Question 5.2.  The MPI transforms in FFTW 1.2 give incorrect
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results/leak memory.
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</A></h2>
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These bugs were corrected in FFTW 1.2.1.  The MPI transforms (really,
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just the transpose routines) in FFTW 1.2 had bugs that could cause
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errors in some situations.  
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<h2><A name="testsingbug">
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Question 5.3.  The test programs in FFTW 1.2.1 fail when I change FFTW
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to use single precision.
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</A></h2>
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This bug was fixed in FFTW 1.3.  (Older versions of FFTW did
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work in single precision, but the test programs didn't--the error
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tolerances in the tests were set for double precision.)
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<h2><A name="teststoobig">
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Question 5.4.  The test program in FFTW 1.2.1 fails for n &gt;
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46340.
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</A></h2>
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This bug was fixed in FFTW 1.3.  FFTW 1.2.1 produced the right answer,
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but the test program was wrong.  For large n, n*n in the naive
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transform that we used for comparison overflows 32 bit integer
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precision, breaking the test.  
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<h2><A name="linuxthreads">
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Question 5.5.  The threaded code fails on Linux Redhat
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5.0
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</A></h2>
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We had problems with glibc-2.0.5.  The code should work with
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glibc-2.0.7.  
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<h2><A name="bigrfftwnd">
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Question 5.6.  FFTW 2.0's rfftwnd fails for rank &gt; 1 transforms
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with a final dimension &gt;= 65536.
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</A></h2>
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This bug was fixed in FFTW 2.0.1.  (There was a 32-bit integer
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overflow due to a poorly-parenthesized expression.)
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<h2><A name="primebug">
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Question 5.7.  FFTW 2.0's complex transforms give the wrong results
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with prime factors 17 to 97.
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</A></h2>
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There was a bug in the complex transforms that could cause incorrect
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results under (hopefully rare) circumstances for lengths with
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intermediate-size prime factors (17-97).  This bug was fixed in FFTW
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2.1.1.  
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<h2><A name="mpichbug">
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Question 5.8.  FFTW 2.1.1's MPI test programs crash with
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MPICH.
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</A></h2>
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This was fixed in FFTW 2.1.2.  The 2.1/2.1.1 MPI test programs crashed
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when using the MPICH implementation of MPI with the
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<code>ch_p4</code> device (TCP/IP); the transforms themselves worked fine.  (The source
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of the bug was some strange constraints that MPICH imposes on access
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to the program argument list.) <hr>
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Back: <a href="section4.html" rev=precedes>Internals of 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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