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MathGroup Archive 1999

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Re: Fourier and FFT: Powers of 2 only?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15911] Re: Fourier and FFT: Powers of 2 only?
  • From: jenningsj at mail.utexas.edu (Jim Jennings)
  • Date: Wed, 17 Feb 1999 23:33:50 -0500
  • Organization: The University of Texas at Austin
  • References: <7a29pk$1pm@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <7a29pk$1pm at smc.vnet.net>, "Peltio" <pelt.ioNOS at PAMiol.it> wrote:

>Since FFT procs work best with sets of points whose number is a power of
>2, what does Fourier[] do when it's fed a set of, say, 200 points? Will
>it extend to 256 by adding zeros, or split it in subsets that are power
>of 2, or whatever?
 
Fourier[] definately works on any number of points without zero padding. 
I'm not sure how it works, but I suspect it has some kind of adaptive
algorithm that breaks up the list into the smallest number of power 2
lists as possible.  I also suspect that the speed of Fourier[] depends on
how "close" your list is to a simple integer power of 2, but I have not
tested it.  In my applicaions it has always been fast enough that I
haven't bothered to think about it.

-- 
Jim Jennings                                
Research Associate              jenningsj at mail.utexas.edu
Bureau of Economic Geology      (512) 471-4364 (voice)
University of Texas at Austin   (512) 471-0140 (fax)


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