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Re: n-point FFT [message #22606 is a reply to message #22601]

Tue, 21 November 2000 00:00

Paul van Delst
Messages: 364
Registered: March 1997

Senior Member

Paul Woodford wrote:
>
> In article <onzoit8fai.fsf@cow.physics.wisc.edu>,
> craigmnet@cow.physics.wisc.edu wrote:
>
>> It's very easy to
>> do any needed zero-padding yourself (ie, fft([x, fltarr(nzeros)]) ).
>
> Easy, but inconvenient. I also missed the Matlab notation when I
> switched to IDL, and finally hacked a small "efft" function to recreate
> it.

Different strokes, but I would never recommend this sort of thing mostly because too many
times I've seen (both others and myself) get in trouble with FFT's because something I or
someone else assumed about the particular FFT implementation (fortran, idl, matlab, C,
various flavours - take your pick) was wrong (or non-portable). Particularly when it comes
to specifying exactly where the Nyquist point is.

Thus, I would always hope that my colleagues are painstakingly clear about how many points
they expect to have in, and with how many zeros they padded, their spectra(um).

> I keep forgetting to send this feature request to RSI...

I wouldn't consider it a feature, but a user bug waiting to happen...... +/- 1 point
errors in FFTs can be capriciously subtle :o(

BTW, I'm not bitter...no, not at all (snuckin' fessin' rotten rasterdly FFTs.....)

:o)

paulv

--
Paul van Delst Ph: (301) 763-8000 x7274
CIMSS @ NOAA/NCEP Fax: (301) 763-8545
Rm.207, 5200 Auth Rd. Email: pvandelst@ncep.noaa.gov
Camp Springs MD 20746

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[Message index]

		Re: n-point FFT By: tandp on Tue, 21 November 2000 00:00
		Re: n-point FFT By: Paul van Delst on Tue, 21 November 2000 00:00
		Re: n-point FFT By: davidf on Tue, 21 November 2000 00:00
		Re: n-point FFT By: Paul Woodford on Tue, 21 November 2000 00:00
		Re: n-point FFT By: Craig Markwardt on Tue, 21 November 2000 00:00

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