Intel® oneAPI Math Kernel Library Developer Reference - Fortran
The section provides a brief reference for the FFTW 2.x C interface. For details please refer to the original FFTW 2.x documentation available at www.fftw.org.
Each FFTW function has its own wrapper. Some of them, which are not expressly listed in this section, are empty and do nothing, but they are provided to avoid link errors and satisfy the function calls.