topic FFT library and allocatable arrays in Intel® oneAPI Math Kernel Library

FFT library and allocatable arrays

John_Kornak — Fri, 19 Nov 2010 01:13:10 GMT

Hi,

I would appreciate any help I can get with the following:

I would like to be able to perform 2D fft on allocatable arrays, but the problem is that I need to have them as 1-D arrays for the Intel Math Kernel FFT library. The solution given in the manual is to use the equivalence statement but that doesn't work for dynamic arrays. I can think of 2 very clunky solutions:

1) Convert matrices to 1-D before DFT and then back to 2D (but I guess this has considerable overhead?)
2) Index all arrays as 1-D. (likely to lead to a lot of bugs)

I would appreciate any more elegant and efficient solution that I can get!

I am using ifort 11.1 on an iMac with an intel Core i7 processor and running Snow Leopard version 10.6.5. I am embarrased to say that I am not sure how to figure out what version of the math kernel I have but I installed the latest version around a month ago.

Thanks

John

FFT library and allocatable arrays

Dmitry_B_Intel — Fri, 19 Nov 2010 04:03:00 GMT

Hi John,

This issue can be worked around as follows:

[fortran]real input(:,:)
complex output(:,:)
allocate(input(M,N), output(M/2+1,N))
...
s = DftiComputeForward(desc, input(:,1), output(:,1))
[/fortran]

This technique assumes that compiler will simply pass pointers to the i/o arrays to the compute funcion. This may not work with array sections, like input(1:100:2,1).

MKL version can be printed with this example (see also examples/servicefuncsf in your MKL installation)

[fortran]program mklversion
  character*(200) :: MKLGetVersionString
  external MKLGetVersionString
  print *, trim(MKLGetVersionString())
end program mklversion
[/fortran]

Thanks
Dima

FFT library and allocatable arrays

Todd_R_Intel — Fri, 19 Nov 2010 19:03:07 GMT

Here are two more ways that you can find out the version of Intel MKL you're using:

If you know the compiler version and update number then you can use the table in our knowledgebase with corresponding library versions. There are now two tables actually: one for the compiler pro line (which it sounds you're currently using) and one for the new Intel Composer XE 2011 products.
In the doc directory open the mklsupport* file.

Todd

FFT library and allocatable arrays

John_Kornak — Tue, 23 Nov 2010 22:40:17 GMT

Sorry for the delay reporting back. It took me a while to get back to this project.

Thank you very much Dmitry and Todd. Your solutions worked perfectly for me.

Cheers

John