Sorry I didn't catch this earlier. On a 64-bit system it's really just your available memory on your particular system. You need enough free memory to hold a bit over 2x the storage space for the array itself (as a complex number, so 4x if you're transforming a real array), after you round the dimensions up to the nearest power of two. I've done a fair number of 1024x1024x256 floating-point 3-D FFTs with fftnd. For some reason, fftnd requires the full FFT buffer size for each dimension (that could/should be fixed, but it's easier to buy RAM), so that is 12 GiB (0.25GiB x 4 x 2 x 2 x 3).
If you're close to your system RAM size you could run into fragmentation issues since the FFT buffers have to be contiguous in the address space and you've presumably been mallocking and freeing hunks of memory all over the place. In that case you can push the variable out to storage (e.g. as a FITS file), then Fourier transform it with a standalone script and slurp up the result in your main script. That lets the standalone script have its own address space independent of the original one. But that's just a workaround for the main issue, which is that you need a ton of RAM to transform large arrays, even with the FFT. On Feb 13, 2013, at 5:09 AM, Chris Marshall <[email protected]> wrote: > I don't know the maximum but if you > pick something with a smaller number > of prime factors, you should be able > to do a larger FFT (within your memory > and pdl size limits). > > You could try PDL::FFTW but you > will need to install version 2 of the > FFTW library. > > --Chris > > On Wed, Feb 13, 2013 at 3:35 AM, Frank Boers <[email protected]> wrote: >> Dear PDLs, >> what is the maximum number of elements PDL::FFT can process? >> >> use PDL::FFT >> >> $data=random(8000000) >> >> realfft($data) >> >> $data=random(8100000) >> >> realfft($data) >> Error: fftradix() - exceeded number of factors >> Error: fftradix() - insufficient memory. >> >> >> best regards >> Frank >> >> -- >> Frank Boers >> Institute of Neuroscience and Medicine - 4 >> Medical Imaging Physics >> Forschungszentrum Juelich GmbH >> 52425 Juelich >> phone: +49 - (0)2461-61-6005 >> fax : +49 - (0)2461-61-2820 >> email: [email protected] >> http://www.fz-juelich.de/inm/inm-4/DE/Forschung/MEG-Physik/_node.html >> >> >> >> ------------------------------------------------------------------------------------------------ >> ------------------------------------------------------------------------------------------------ >> Forschungszentrum Juelich GmbH >> 52425 Juelich >> Sitz der Gesellschaft: Juelich >> Eingetragen im Handelsregister des Amtsgerichts Dueren Nr. HR B 3498 >> Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher >> Geschaeftsfuehrung: Prof. Dr. Achim Bachem (Vorsitzender), >> Karsten Beneke (stellv. Vorsitzender), Prof. Dr.-Ing. Harald Bolt, >> Prof. Dr. Sebastian M. Schmidt >> ------------------------------------------------------------------------------------------------ >> ------------------------------------------------------------------------------------------------ >> >> _______________________________________________ >> Perldl mailing list >> [email protected] >> http://mailman.jach.hawaii.edu/mailman/listinfo/perldl > > _______________________________________________ > Perldl mailing list > [email protected] > http://mailman.jach.hawaii.edu/mailman/listinfo/perldl > _______________________________________________ Perldl mailing list [email protected] http://mailman.jach.hawaii.edu/mailman/listinfo/perldl
