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MathGroup Archive 1999

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Re: FourierTransform Bug V4

  • To: mathgroup at smc.vnet.net
  • Subject: [mg20553] Re: FourierTransform Bug V4
  • From: Jane.M.Manderscheid at lerc.nasa.gov (Jane M Manderscheid)
  • Date: Sat, 30 Oct 1999 00:14:04 -0400
  • Organization: NASA Lewis Research Center
  • References: <7v3dqn$64d@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

I don't know how to fix it, but the problem may be due to the usage of 
DiracDelta functions rather than Fourier transforms. Try the following 
command: 
Integrate[2 DiracDelta[w-2x],x]
-1+UnitStep[-w+2 x]
Change the w to y and you'll get a different answer:
Integrate[ 2 DiracDelta[y-2 x],x]
UnitStep[2 x-y]
These results were obtained from V. 4 on unix platforms.  Version 3 works 
correctly.  I emailed Wolfram a week ago but have not received a response.

Jane Manderscheid
NASA Glenn Research Center

In article <7v3dqn$64d at smc.vnet.net>, lwalker701 at earthlink.net says...
>
>FourierTransform of v4 returns incorrect values.  For
>example, the following is computed in version 4:
>
>FourierTransform[UnitStep[t], t, w, FourierParameters ->
>{1,-1}]
>
>= -(I/w) - Pi*DiracDelta[w]
>
>But version 3 correctly returns
>
>-(I/w) + Pi*DiracDelta[w]
>
>How can I fix this?  Perhaps Unprotect[FourierTransform]...
>
>Thanks,
>Lawrence
>
>
>--
>
>
>------------------------------------------------------------
>
>     (\___/)     The fear of the LORD is the beginning of
>     (o\ /o)     wisdom: a good understanding have all they
>    /|:.V.:|\    that do his commandments: his praise
>    \\::::://    endureth for ever.              Psa 111:10
>-----`"" ""`------------------------------------------------
>
>        Lawrence A. Walker Jr., M.Eng./Ph.D. Candidate
>                   Morgan State University
>          Clarence M. Mitchell School of Engineering
> COMSARE (Center Of Microwave/Satellite And RF Engineering)
>           Rm: 306-Schafer     Phone: (443)885-1453
>------------------------------------------------------------
>
>
>
>



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