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Re: FourierTransform

• To: mathgroup at smc.vnet.net
• Subject: [mg52525] Re: FourierTransform
• From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
• Date: Wed, 1 Dec 2004 05:57:39 -0500 (EST)
• Organization: Uni Leipzig
• References: <cohj7g$1nk$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

why do you think that FourierTransform[f'[x], x, k]
for a general function is convergent ?
It is simple to add the rule explicit by

expr = FourierTransform[f'[x], x, k];

iKnowItIsConvergent =
FourierTransform[a_.*Derivative[n_][f_][x_], x_, k_] :>
a*(-I k)^n FourierTransform[f[x], x, k];

expr /. iKnowItIsConvergent



Regards

  Jens


"Dr A.H. Harker" <a.harker at ucl.ac.uk> schrieb im Newsbeitrag 
news:cohj7g$1nk$1 at smc.vnet.net...
> In Version 4 Mathematica was smart enough to know that
>
> FourierTransform[f'[x], x, k]
>
> should give
>
> -\[ImaginaryI] k FourierTransform[f[x], x, k].
>
> Version 5 seems no longer to do this -- a nice classroom demonstration and
> a valuable method of solving differential equations down in flames.
>
>  Why is this?
>
>
> Tony Harker (Dr A.H. Harker)
> Deputy Head of Department
> Deputy Head, Condensed Matter and Materials Physics Group
> Department of Physics and Astronomy
> University College London
> Gower Street
> LONDON
> WC1E  6BT
> (44)(0)207 679 3404
> a.harker at ucl.ac.uk
>
>
>