[GRASS5] i.fft segemntation fault

Stephan Holl sholl at gmx.net
Fri Jun 11 08:51:52 EDT 2004

Hello Glynn, 

On Fri, 11 Jun 2004 13:10:18 +0100 Glynn Clements
<glynn.clements at virgin.net> wrote:

> Stephan Holl wrote:
> > > The memory requirements could be reduced to two doubles per cell
> > > (without scaling up to a power of two) if i.fft used FFTW
> > > directly, rather than using the fft() interface. Or to two floats
> > > per cell if FFTW was built to use float instead of double.
> >  
> > As this seems to be an option for reducing the memory-needs a
> > little, is this a doable task? I think it would be benefit when FFTW
> > is used directly instead of fft(). Correct me when I am wrong,
> > please...
> > 
> > If so, how much work would that be?
> Not much; the fft() function itself is trivial, and much of that is
> copying the data between the separate real/imaginary arrays and the
> single complex array used by FFTW, which wouldn't be necessary if you
> were calling FFTW directly.
> Note: the fft() function is in src/libes/gmath/fft.c.

As I am more a GIS-user than a programmer I cannot modify
src/libes/gmath/fft.c to use FFTW directly even if fft() seems trivial.
I understand whats going on there, but nothing more...

Perhaps anybody else with more programming-skills can implement this?!
Stephan Holl

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