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Re: Different results with FourierTransform[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97633] Re: Different results with FourierTransform[]
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Tue, 17 Mar 2009 05:01:34 -0500 (EST)
  • Organization: Uni Leipzig
  • References: <gpl5sh$ou6$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

and more surprising I have a third one, and this is the
correct one

Integrate[Tanh[x]*Exp[I*x*p], {x, -Infinity, Infinity}]

gives

Integrate::idiv:Integral of E^(I*p*x) Tanh[x] does not converge on
{-Infinity,Infinity}

Regards
   Jens

Wieland Brendel wrote:
> Dear reader,
> I somewhat stumbled over the following behaviour of mathematica: I tried 
> to calculate the fouriertransform of Tanh[x]. I did this in two ways:
> 
> 1. Directly:
> InverseFourierTransform[Tanh[x], x, p]
> 
> 2. Indirectly:
> InverseFourierTransform[Tanh[B x], x, p]
> 
> where I set B -> 1 in the end.
> 
> However, the result between the two approaches differs: Whereas in the 
> first approach I get a complex number (with both real and imaginary part 
> being non-zero for almost all values of p), the result in the second 
> approach yields NO real part; the imaginary part however is the same as 
> in the first approach. Is there any explanation for this behaviour?
> 
> Thanks a lot in advance! I am really stuck with that...
> Wieland
> 
> 


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