5.2.4 3D FFT of three-dimensional arrays of data

The routines documented here compute the three-dimensional discrete Fourier transforms (DFT) of a three-dimensional array of complex numbers in either single or double precision arithmetic. The 3D DFT is computed using a highly-efficient FFT algorithm.

Please note that at Release 2.7 of ACML it has been necessary to modify slightly the interfaces of two of the expert FFT drivers introduced at Release 2.2 of ACML. The two routines are CFFT3DX and ZFFT3DX. The changes are required to permit the optimization of these routines by adding an initialization stage which can then use the plan generator (MODE=100) to select the optimal plan. User codes that called CFFT3DX or ZFFT3DX using a release of ACML prior to 2.7 will need to be modified in one of two ways. Calls to CFFT3DX/ZFFT3DX with MODE = -1 or 1 can be fixed for ACML Release 2.7 and later by either:

• preceding the call with a call setting MODE = 0 (default initialization), or MODE = 100 (initialization using plan generator); or,
• doubling the MODE argument value to MODE = -2 or 2 respectively (thus incorporating default initialization).

Additionally, the minimum length of the communication (work)space arrays in CFFT3DX and ZFFT3DX has been increased by 100 to allow for plan storage. Please consult the individual routine documents for full details on their use.

• ZFFT3D: Three-dimensional Double Complex FFT, simple driver
• CFFT3D: Three-dimensional, single precision, Complex FFT, simple driver
• ZFFT3DX: Three-dimensional Double Complex FFT, expert driver 1
• CFFT3DX: Three-dimensional, single precision, Complex FFT, expert driver 1
• ZFFT3DY: Three-dimensional Double Complex FFT, expert driver 2
• CFFT3DY: Three-dimensional, single precision, Complex FFT, expert driver 2