Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

ID 766686
Date 7/13/2023
Public

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DFTI_ORDERING

Some FFT algorithms apply an explicit permutation stage that is time consuming [4]. The exclusion of this step is similar to applying an FFT to input data whose order is scrambled, or allowing a scrambled order of the FFT results. In applications such as convolution and power spectrum calculation, the order of result or data is unimportant and thus using scrambled data is acceptable if it leads to better performance. The following options are available in Intel® oneAPI Math Kernel Library (oneMKL):

  • DFTI_ORDERED: Forward transform data ordered, backward transform data ordered (default option).

  • DFTI_BACKWARD_SCRAMBLED: Forward transform data ordered, backward transform data scrambled.

Table "Scrambled Order Transform" tabulates the effect of this configuration setting.

Scrambled Order Transform
 

DftiComputeForward

DftiComputeBackward

DFTI_ORDERING

Input → Output

Input → Output

DFTI_ORDERED

ordered → ordered

ordered → ordered

DFTI_BACKWARD_SCRAMBLED

ordered → scrambled

scrambled → ordered

NOTE:

The word "scrambled" in this table means "permit scrambled order if possible". In some situations permitting out-of-order data gives no performance advantage and an implementation may choose to ignore the suggestion.

See Also