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 > > >