       Re: Fourier transform

• To: mathgroup at smc.vnet.net
• Subject: [mg13928] Re: [mg13923] Fourier transform
• From: "Jens-Peer Kuska" <kuska at linmpi.mpg.de>
• Date: Tue, 8 Sep 1998 02:52:28 -0400
• Sender: owner-wri-mathgroup at wolfram.com

```Hi Andrea,

Fourier[] implements a numerical fast fourier transform. That means that
the data passed to Fourier[] are  the function values f(t) on the
interval t in [0,2Pi) with constant increment. The data are assumed to
be periodic in t with period 2Pi.

Assume You have a solution ndsol={y[t]->InterpolatingFunction[<>][t]}
With
fun=y[t] /. ndsol;
pointNo=256;
inc=N[2Pi]/(pointNo-1);
data=Table[fun,{t,0.,2.*Pi,inc}];

You get Your data set and can use

fftdata=Fourier[data]

to make the transformation.
For other time intervals You need a proper scaleing of the t-variable.

Hope that helps
Jens

-----Original Message-----
From: Andrea Cherubini <Andrea.Cherubini at roma1.infn.it> To:
mathgroup at smc.vnet.net
Subject: [mg13928] [mg13923] Fourier transform

>Hello,
>
>how can I do the Fourier Transform of NDSolve results?
>
>Thanks, Andrea
>
>
>

```

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