FFT support libraries

Steffen Persvold sp at scali.no
Thu Jul 26 23:12:03 EDT 2001


Steffen Persvold wrote:
> 
> Greg Lindahl wrote:
> >
> > On Thu, Jul 26, 2001 at 10:10:03PM +0200, Steffen Persvold wrote:
> >
> > > I'm trying to port a fortran application using SGI FFT functions
> > > (complib.sgimath) to Linux. The only FFT functions that are used are
> > > zfft1di and zfft1d. I understand that these are double complex
> > > functions and I've downloaded the double precision fftpack from
> > > netlib.org (dfftpack). However, the dfftpack routines zffti and
> > > zfft{f,b} doesn't seem to match the SGI functions.
> >
> > Welcome to Fourier Transform Hell. No 2 libraries are the same, for
> > no good reason.
> >
> > > Now, here I guess that the direction parameter to ZFFT1D is just a
> > > way to decide wether to use a forward or a backward FFT, but what is
> > > the parameter after E_SLICE ??.
> >
> > The manpage says that the parameter after E_SLICE is the stride of the
> > array, which will be undoubtedly 1 in your code. This is a fairly
> > unusual feature in a fft library.
> 
> Thanks Greg,
> 
> Now where did you find this manpage ? Is it online ??
> 
Never mind, I found it after a while of searching :

http://www.ac3.com.au/cgi-bin/irix/man/usr/share/catman/p_man/cat3/complib/fft1d.z

Now, any idea why dfftpack needs the workspace to be 4
*n+15 and SGI libraries only n+15 ??

Regards,
-- 
  Steffen Persvold               Systems Engineer
  Email : mailto:sp at scali.no     Scali AS (http://www.scali.com)
  Tlf   : (+47) 22 62 89 50      Olaf Helsets vei 6
  Fax   : (+47) 22 62 89 51      N-0621 Oslo, Norway

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