Intel® Math Kernel Library (Intel® MKL) offers two collections of wrappers for the FFTW interface (www.fftw.org). The wrappers are the superstructure of FFTW to be used for calling the Intel MKL Fourier transform functions. These collections correspond to the FFTW versions 2.x and 3.x and the Intel MKL versions 7.0 and later.
These wrappers enable using Intel MKL Fourier transforms to improve the performance of programs that use FFTW without changing the program source code. See the "FFTW Interface to Intel® Math Kernel Library" appendix in the Intel MKL Developer Reference for details on the use of the wrappers.
For ease of use, FFTW3 interface is also integrated in Intel MKL.