Changing the sign of complex exponential in DftiComputeForward()

[Amir_S_]

Hi,

I am currently working with FFT tools of MKL 10.3.12, specifically Dfti and Fortran interface. In my Forward transform, complex exponentials have positive sign as opposed to the default negative sign. Although I saw in this article: "https://software.intel.com/en-us/articles/the-intel-math-kernel-library-and-its-fast-fourier-transform-routines" that changing sign is provided in mkl_Dfti, I couldn't find any relevant parameter for that. After checking the original file "mkl_dfti.f90", I noticed that DFTI_FORWARD_SIGN is not implemented yet. So my question is if the newer versions have this facility and if not what is your proposed solution to take advantage of using Dfti (like using complex conjugate even storage) while having positive sign in forward transform.

Many thanks in advance

[Evarist_F_Intel]

Hi Amir,

Unfortunately we still did not implement an ability to modify exponentials sign for forward and backward transforms.

Some obvious workarounds are: 1) if you are computing complex-to-complex FFT then changing the sign is equivalent to calling DftiComputeBackward instead of DftiComputeForward and vice a verse. 2) if you are computing real-to-complex FFT then changing the sign is equivalent to complex conjugation of the complex-valued output.