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MathGroup Archive 2005

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Re: fourier transform

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61214] Re: fourier transform
  • From: Torsten Coym <torsten.coym at eas.iis.fraunhofer.de>
  • Date: Thu, 13 Oct 2005 01:39:25 -0400 (EDT)
  • Organization: Fraunhofer Gesellschaft (http://www.fraunhofer.de/)
  • References: <dii9qs$9q1$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Take a look at Mathematica's help: Fourier[data] expects data to be a
list of complex numbers, not pairs of time and amplitude.

I assume that your list is equally spaced in time -- only then a
application of Fourier[] would lead to useful results.

Get rid of the timing information in your data, by replacing every pair
of {time,amplitude} with the amplitude only.

data=yourdata/.{t_,ampl_}->ampl

freqdata=Chop@Fourier[data]

Have a look at Chop[] to suppress small imaginery parts that come from
the numerical process.

Cheers,
Torsten

Masrur Hossain wrote:
> Hi folks
>            I have a list of pairs of numbers like
> 
>   {{1.2, 3.4}, {2.2, 3.6}............}
> The first part is time and second part is amplitude.
> 
> when I do the fourier transform by using
> Fourier[list]
> 
> it gives me list of complex numbers but I expect real numbers
> (i.e . amplitude versus frequency)
> 
> 
> Any help appreciated.
> 
> thanks


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