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Re: Again an FFT question [message #80648 is a reply to message #80647]

Wed, 27 June 2012 09:45

lecacheux.alain
Messages: 325
Registered: January 2008

Senior Member

On 27 juin, 18:33, David Fanning <n...@idlcoyote.com> wrote:
> alx writes:
>> You can use the /CENTER keyword in FFT function since IDL7.1
>
> Well, it was *present* in IDL 7.1. I don't think
> it actually worked until later.
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.idlcoyote.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
>
>

?
IDL> print,fft(cos(2*!pi*findgen(16)/16*3))
( 5.06635e-008, 0.000000)( 8.06580e-008, 3.52675e-008)
(-9.04610e-009, 2.63418e-008)( 0.500000, 1.28007e-007)
(-9.08976e-008, 1.49012e-008)
(-2.65443e-008,-1.35536e-008)( 1.20273e-008, 2.63418e-008)
(-7.60014e-008,-9.51177e-008)( 1.25169e-007, -0.000000)
(-7.60014e-008, 9.51177e-008)
( 1.20273e-008,-2.63418e-008)(-2.65443e-008, 1.35536e-008)
(-9.08976e-008,-1.49012e-008)( 0.500000,-1.28007e-007)
(-9.04610e-009,-2.63418e-008)
( 8.06580e-008,-3.52675e-008)
IDL> print,fft(cos(2*!pi*findgen(16)/16*3),/CENTER)
( 1.25169e-007, -0.000000)(-7.60014e-008, 9.51177e-008)
( 1.20273e-008,-2.63418e-008)(-2.65443e-008, 1.35536e-008)
(-9.08976e-008,-1.49012e-008)
( 0.500000,-1.28007e-007)(-9.04610e-009,-2.63418e-008)
( 8.06580e-008,-3.52675e-008)( 5.06635e-008, 0.000000)
( 8.06580e-008, 3.52675e-008)
(-9.04610e-009, 2.63418e-008)( 0.500000, 1.28007e-007)
(-9.08976e-008, 1.49012e-008)(-2.65443e-008,-1.35536e-008)
( 1.20273e-008, 2.63418e-008)
(-7.60014e-008,-9.51177e-008)
Both statements give expected results: i.e. non zero values at
positions 3 and 13 (CENTER=0) or 5 and 11 (CENTER=1).
alx.

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[Message index]

		Re: Again an FFT question By: Kenneth P. Bowman on Thu, 28 June 2012 06:07
		Re: Again an FFT question By: Helder Marchetto on Thu, 28 June 2012 02:00
		Re: Again an FFT question By: lecacheux.alain on Wed, 27 June 2012 09:45
		Re: Again an FFT question By: lecacheux.alain on Wed, 27 June 2012 09:45
		Re: Again an FFT question By: David Fanning on Wed, 27 June 2012 09:33
		Re: Again an FFT question By: lecacheux.alain on Wed, 27 June 2012 09:22
		Re: Again an FFT question By: Kenneth P. Bowman on Wed, 27 June 2012 08:53

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