FFTW Frequently Asked Questions with Answers

This is the list of Frequently Asked Questions about FFTW, a collection of fast C routines for computing the Discrete Fourier Transform in one or more dimensions.

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.

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Matteo Frigo and Steven G. Johnson / [email protected] - 14 September 2021
Extracted from FFTW Frequently Asked Questions with Answers, Copyright © 2021 Matteo Frigo and Massachusetts Institute of Technology.