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?
Section 2. Installing FFTW
Q2.1. Which systems does FFTW run on?
Q2.2. Does FFTW run on DOS/Windows?
Q2.3. My compiler crashes when compiling FFTW.
Q2.4. Which language is FFTW written in?
Q2.5. Can I call FFTW from FORTRAN?
Q2.6. Can I call FFTW from C++?
Q2.7. Why isn't FFTW written in FORTRAN/C++?
Q2.8. How do I compile FFTW to run in single precision?
Section 3. Using FFTW
Q3.1. FFTW gives results different from my old FFT.
Q3.2. Can I save FFTW's plans?
Q3.3. Why does your inverse transform return a scaled result?
Q3.4. How can I make FFTW put the origin (zero frequency) at the center of its output?
Section 4. Internals of FFTW
Q4.1. How does FFTW work?
Q4.2. Why is FFTW so fast?
Q4.3. What is this wisdom thing?
Q4.4. Why do you use wisdom? I just wanted to save a plan.
Q4.5. Why are there so many ways to import/export wisdom?
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.

Matteo Frigo and Steven G. Johnson / fftw@theory.lcs.mit.edu - 06 May 1998