Re: Gsl FFT <-> FFTW compatibility

On Mon, 25 Jul 2011, Stefan Westerfeld wrote:

On Mon, May 16, 2011 at 11:35:32PM +0200, timj gnu org wrote:

However, there are the real variants, which used to work like that

fftar: real data -> fftac -> post processing -> complex output
fftsr: complex data -> pre processing -> fftsc -> real output

I changed these to FFTW behaviour by adjusting the (pre/post) processing steps,
so we have

fftar: real data -> old fftac -> post processing* -> complex output
fftsr: complex data -> pre processing* -> old fftsc -> real output

which is

fftar: real data -> fftsc -> post processing* -> complex output
fftsr: complex data -> pre processing* -> fftac -> real output

It would be possible to rederive the post/pre processing from numerical
recipies to do the right thing without still using the old style functions.
However that would be quite a bit of work, so I preferred to do it my way
which relies on the "old fftac" step and the "old fftsc" step.

I see, thanks for the explanation. It seems that you already adapted the
post/pre processing, and given that the real valued fft routines don't
match the complex valued one, I'd guess that you added additional ops in
one or both of the post/pre processing routines which likely make things
slower, right?

  Cu... Stefan

Yours sincerely,
Tim Janik

--- - Founder and CEO of Lanedo GmbH.
Free software author and contributor on various projects.

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