FFTW3 is a C subroutine library with Fortran interfaces for computing complex-to-complex and real-to-complex/complex_to_real single and multidimensional discrete Fourier transforms (DFTs). The library also includes routines to compute discrete cosine and sine transforms (DCTs/DSTs) on even and odd data, respectively.
To use FFTW 3.1.1, load the module fftw or fftw/3.1.1 (3.1.1 is the default).
In FFTW 3.1.1, the single and double precision routine names are unique and, therefore, both libraries automatically appear on the link line when the fftw/3.1.1 module is loaded so that a user's program can call single or double precision routines. The single and double precision libraries are libfftw3f.a and libfftw3.a, respectively.
FFTW 3.1.1 supports the system wide wisdom file (for details, see the FFTW web site, http://www.fftw.org). Cray has added the environment variable FFTW_SYSTEM_WISDOM_DIR, which is set to the location of a particular installation's system wisdom directory. The fftw/3.1.1 module automatically sets this up.
FFTW 3.1.1 and FFTW 2.1.5 cannot be loaded at the same time.
The current release does not include system wisdom in the directory pointed to by FFTW_SYSTEM_WISDOM_DIR, as is set up by the fftw/3.1.1 module. This will be included in a future release. In line with recommendations from the FFTW authors, users are encouraged, however, to generate and use their own FFTW3 wisdom.