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)