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