Re: fft question

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.



-------- 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


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?


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