Using multiple DFTI DESCRIPTOR (FFT in MKL)

[Chris_L_1]

Is it possible to create and commit several different DFTI descriptor and re-use them later (the FFT of different sizes will be called many times, and creating the descriptor and free it for each call seems not efficient). In other words, can the descriptor be created/committed and then saved in some arrays?

[Gennady_F_Intel]

yes, that's possible.

[Chris_L_1]

Thanks. It's good to know. I have the following section of code. My question is how to extend it to the cases with much more than 3 lengths? I tried to save the descriptor in an array,  it compiles and does now run.

      Use MKL_DFTI
      integer ier, n, k
      complex cx(1000)
      type(DFTI_DESCRIPTOR), POINTER ::  HD1, HD2, HD3, HDk
      type(DFTI_DESCRIPTOR) HD(3)

      ier=DftiCreateDescriptor(HD1,DFTI_SINGLE,DFTI_COMPLEX,1, 32)
      ier=DftiCreateDescriptor(HD2,DFTI_SINGLE,DFTI_COMPLEX,1,132)
      ier=DftiCreateDescriptor(HD3,DFTI_SINGLE,DFTI_COMPLEX,1,232)

      ier=DftiCommitDescriptor(HD1)
      ier=DftiCommitDescriptor(HD2)
      ier=DftiCommitDescriptor(HD3)

      HD(1) = HD1
      HD(2) = HD2
      HD(3) = HD3

      do k = 1, 3

        n = 32 + 100*(k-1)
        ! ignored : Fill cx(1) ... cx(n)

! The following does not work:
!       HDk = HD(k)

! But this is OK
        if(k.eq.1 ) HDk=HD1
        if(k.eq.1 ) HDk=HD2
        if(k.eq.1 ) HDk=HD3

        ier = DftiComputeForward( HDk, cx )

      end do

      ier = DftiFreeDescriptor(HD1)

[Chris_L_1]

Error correction: The pointer assignments (in the above) are

        if(k.eq.1 ) HDk=>HD1
        if(k.eq.2 ) HDk=>HD2
        if(k.eq.3 ) HDk=>HD3

       Are there any way to avoid writing the "if( ... ) ..." statement many times (e.g., ~ 20)?