developed by Matteo Frigo and Steven G. Johnson at MIT
FFTW is a efficient, multi-threaded C subroutine library with fortran interface for computing the discrete Fourier transform (DFT) in one or more dimensions, of arbitrary input size, and of both real and complex data (as well as of even/odd data, i.e. the discrete cosine/sine transforms or DCT/DST). FFTW version 2.1.5 also includes parallel transforms for both shared- and distributed-memory systems. FFTW version 3.0.1 doesn't include parallel transforms for distributed-memory systems