FFTPACK is a package of Fortran-77 subroutines for the Fast Fourier Transform of periodic and other symmetric sequences developed by Paul N. Swarztrauber from the National Center for Atmospheric Research in Boulder, Colorado. The project was sponsored by the National Science Foundation.

The subroutines are transferrable by WWW and FTP from the Netlib site:

http://www.netlib.org/

There are 12 subroutines in the package, plus 7 auxiliary subroutines, which serve to initialize other subroutines, 19 subroutines in total. The essential subroutines are as follows:

**rfftf**- forward transform of a real periodic sequence
**rfftb**- backward transform of a real coefficient array
**ezfftf**- a simplified real periodic forward transform
**ezfftb**- a simplified real periodic backward transform
**sint**- sine transform of a real odd sequence
**cost**- cosine transform of a real even sequence
**sinqf**- forward sine transform with odd wave numbers
**sinqb**- unnormalized inverse of sinqf
**cosqf**- forward cosine transform with odd wave numbers
**cosqb**- unnormalized inverse of cosqf
**cfftf**- forward transform of a complex periodic sequence
**cfftb**- unnormalized inverse of cfftf

See, e.g.,

for more information about those routines.http://beige.ucs.indiana.edu/FFTPACK/doc