A last idea: in order to visualize the spectrum of a "complex" Fourier transform (unlike FFT), you need to calculate the module of the result, which implies squaring the result. [Caution: I think it is called "module" in English.]
Maybe this is the reason for getting only half the image - maybe "complex data" implies the generic Discrete Fourier Transform (DFT), and the result is a spectrum containing complex numbers, which needs a further transformation in order to be displayed - the modulus being displayed instead of the actual DFT. Sincerely, Leonard -------- Original-Nachricht -------- > Datum: Sun, 03 Oct 2010 21:08:00 +0200 > Von: "Leonard Mada" <[email protected]> > An: Jean Brefort <[email protected]>, [email protected] > Betreff: 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. > > Sincerely, > > Leonard > > > -------- Original-Nachricht -------- > > Datum: Sun, 03 Oct 2010 08:41:51 +0200 > > Von: Jean Brefort <[email protected]> > > An: Gnumeric List <[email protected]> > > 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 €/mtl.! Jetzt auch mit > gratis Notebook-Flat! http://portal.gmx.net/de/go/dsl > _______________________________________________ > gnumeric-list mailing list > [email protected] > http://mail.gnome.org/mailman/listinfo/gnumeric-list -- GRATIS: Spider-Man 1-3 sowie 300 weitere Videos! Jetzt freischalten! http://portal.gmx.net/de/go/maxdome _______________________________________________ gnumeric-list mailing list [email protected] http://mail.gnome.org/mailman/listinfo/gnumeric-list
