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MathGroup Archive 1997

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Re: Defining Real expressions

  • To: mathgroup at
  • Subject: [mg8509] Re: Defining Real expressions
  • From: hans.steffani at (Hans Steffani)
  • Date: Thu, 4 Sep 1997 02:19:55 -0400
  • Organization: University of Technology Chemnitz, FRG
  • Sender: owner-wri-mathgroup at

Marco Beleggia <beleggia at> writes:

>I must evaluate an Integral in which I'd like to assign real values to
>some parameters, but I don't know how to do that.

>For example, in the following integral (a Fourier Transform): 

>f[x_,p_]=Integrate[y/(x^2+y^2) Exp[-I p y],{y,-Infinity,Infinity}],

>p should be a real parameter. The output given by Mathematica is
>conditioned to Im[p]==0, such as If[Im[p]==0,....,....], which is not
>easy to handle, and I'd like to avoid this complication.

I do not understand the problem:

Integrate[y/(x^2+y^2) Exp[-I p y],{y,-Infinity,Infinity}]


     2 1/4               Sqrt[p ] Pi
-I (p )    Sqrt[Pi] Sqrt[-----------]
                2        2
          Sqrt[p ] Sqrt[x ]

Maybe ComplexExpand[] helps in your case.

Hans Friedrich Steffani
Institut fuer Elektrische Maschinen und Antriebe, TU Chemnitz-Zwickau
mailto:hans.steffani at

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