FFTW Frequently Asked Questions with Answers

Index

• Section 1. Introduction and General Information
• Q1.1. What is FFTW?
• Q1.2. How do I obtain FFTW?
• Q1.3. Is FFTW free software?
• Q1.4. What is this about non-free licenses?
• Q1.5. In the West? I thought MIT was in the East?
  
  
• Section 2. Installing FFTW
• Q2.1. Which systems does FFTW run on?
• Q2.2. Does FFTW run on Windows?
• Q2.3. My compiler has trouble with FFTW.
• Q2.4. FFTW does not compile on Solaris, complaining about const.
• Q2.5. What's the difference between --enable-3dnow and --enable-k7?
• Q2.6. What's the difference between the fma and the non-fma versions?
• Q2.7. Which language is FFTW written in?
• Q2.8. Can I call FFTW from Fortran?
• Q2.9. Can I call FFTW from C++?
• Q2.10. Why isn't FFTW written in Fortran/C++?
• Q2.11. How do I compile FFTW to run in single precision?
• Q2.12. --enable-k7 does not work on x86-64
  
  
• Section 3. Using FFTW
• Q3.1. Why not support the FFTW 2 interface in FFTW 3?
• Q3.2. Why do FFTW 3 plans encapsulate the input/output arrays and not just the algorithm?
• Q3.3. FFTW seems really slow.
• Q3.4. FFTW slows down after repeated calls.
• Q3.5. An FFTW routine is crashing when I call it.
• Q3.6. My Fortran program crashes when calling FFTW.
• Q3.7. FFTW gives results different from my old FFT.
• Q3.8. FFTW gives different results between runs
• Q3.9. Can I save FFTW's plans?
• Q3.10. Why does your inverse transform return a scaled result?
• Q3.11. How can I make FFTW put the origin (zero frequency) at the center of its output?
• Q3.12. How do I FFT an image/audio file in foobar format?
• Q3.13. My program does not link (on Unix).
• Q3.14. I included your header, but linking still fails.
• Q3.15. My program crashes, complaining about stack space.
• Q3.16. FFTW seems to have a memory leak.
• Q3.17. The output of FFTW's transform is all zeros.
• Q3.18. How do I call FFTW from the Microsoft language du jour?
• Q3.19. Can I compute only a subset of the DFT outputs?
• Q3.20. Can I use FFTW's routines for in-place and out-of-place matrix transposition?
  
  
• Section 4. Internals of FFTW
• Q4.1. How does FFTW work?
• Q4.2. Why is FFTW so fast?
  
  
• Section 5. Known bugs
• Q5.1. FFTW 1.1 crashes in rfftwnd on Linux.
• Q5.2. The MPI transforms in FFTW 1.2 give incorrect results/leak memory.
• Q5.3. The test programs in FFTW 1.2.1 fail when I change FFTW to use single precision.
• Q5.4. The test program in FFTW 1.2.1 fails for n > 46340.
• Q5.5. The threaded code fails on Linux Redhat 5.0
• Q5.6. FFTW 2.0's rfftwnd fails for rank > 1 transforms with a final dimension >= 65536.
• Q5.7. FFTW 2.0's complex transforms give the wrong results with prime factors 17 to 97.
• Q5.8. FFTW 2.1.1's MPI test programs crash with MPICH.
• Q5.9. FFTW 2.1.2's multi-threaded transforms don't work on AIX.
• Q5.10. FFTW 2.1.2's complex transforms give incorrect results for large prime sizes.
• Q5.11. FFTW 2.1.3's multi-threaded transforms don't give any speedup on Solaris.
• Q5.12. FFTW 2.1.3 crashes on AIX.