Re: fft question

["Leonard Mada" <discoleo gmx net>]

Dear Jean,

FFT generates symmetric spectra - basically symmetric mirror images.
[The frequencies are mirrored against the central 0.]

This seems to be the case in the "real" image.

While the "complex" image seems to include only one half,
which is the usual way to represent the NMR spectrum.
[and more generally any frequency-power spectrum in real life]

I do not have though access to go_fft, and I am unsure what
"complex data" in your post means.

Sincerely,

Leonard


-------- Original-Nachricht --------
> Datum: Sun, 03 Oct 2010 08:41:51 +0200
> Von: Jean Brefort <jean brefort normalesup org>
> An: Gnumeric List <gnumeric-list gnome org>
> Betreff: fft question

> Hi,
>
> I'm a bit puzzled about the output of the go_fft function (actually the
> same code as what we have in gnumeric, may be gnumeric might use the
> goffice version?). I'm trying to use it to transform an NMR FID to a
> spectrum. When I use only the real data, things give the expected
> result, but I do not understand the output when I use the complex data
> input (see attached images). Is there some FFT expert around?
>
> Regards,
> Jean

-- 
GMX DSL Doppel-Flat ab 19,99 &euro;/mtl.! Jetzt auch mit 
gratis Notebook-Flat! http://portal.gmx.net/de/go/dsl