       RE: Re: Fourier frequencies

• To: mathgroup at smc.vnet.net
• Subject: [mg43524] RE: [mg43428] Re: [mg43401] Fourier frequencies
• From: "kimsj" <kimsj at mobile.snu.ac.kr>
• Date: Fri, 19 Sep 2003 03:41:48 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```> -----Original Message-----
> From: Sseziwa Mukasa [mailto:mukasa at jeol.com]
To: mathgroup at smc.vnet.net
> Sent: Wednesday, September 17, 2003 8:59 PM
> To: mathgroup at smc.vnet.net
> Subject: [mg43524] [mg43428] Re: [mg43401] Fourier frequencies
>
>
> On Friday, August 29, 2003, at 07:16 AM, akpovo wrote:
>
> > Hello to all,
> > How possible is it to compute a fourier transform of a data set
{t,x}
> > in
> > order to have the fourier coefficient and the corresponding
frequency?
> > Tahnks
> >
> >
>
> The Fourier Transform is computed as normal
>
> Fourier[x]
>
> Traditionally the 0 frequency is placed in the center of the spectrum,
> after an FFT though it is at the left so we rotate the data:
>
> RotateRight[Fourier[x],Quotient[Length[x],2]
>
> The frequencies are determined from the time with the following
function
>
> freq[t_]:=With[{tau=t[]-t[],n=Length[t]},Table[-tau/2+i/(n
> tau),{i,0,n-1}]
>
> You can the use ListPlot to get the spectrum, assuming the data is in
> the list x and the times in the list t
>
>
ListPlot[Transpose[{freq[t],RotateRight[Fourier[x],Quotient[Length[x],2]
> ]}],PlotJoined->True]
>
> Regards,
>
> Ssezi

Akpovo,

If you want to do symbolic Fourier transform sometimes besides discrete
Fourier transform, you may use the function FourierTransform[] on the
contrast to Fourier[].

--
Regards,
---
James (txdiversity at hotmail.com)
- Private opinions: These are not the opinions from my affiliation.

```

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