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Re: Re: Defining Real Expressions


> From raya at mech.ed.ac.uk Sun Sep  7 08:58:49 1997
> Date: Sat, 6 Sep 1997 23:16:07 -0400
> From: Raya Firsov-Khanin <raya at mech.ed.ac.uk>
To: mathgroup at smc.vnet.net
> To: mathgroup at smc.vnet.net
> Subject: [mg8597] [mg8535] Re: Defining Real Expressions
> 
> Marco Beleggia wrote:
> 
> <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.
> 
> <Is it possible ?
> 
> The simplest way to deal with this is to declare
> 
> p/:Im[p]=0
> 
> Then, f[x, p] will give you an answer (if Arg[x^2]!=\[Pi]).
> 
> -------		
> 		              Raya Khanin
> 

Hi,

  look on the Assumptions Option of Integrate[] with some thing like
  
  Integrate[
    y/(x^2+y^2) Exp[-I p y],
    {y,-Infinity,Infinity},
    Assumptions->
      {Im[p]==0,Im[x]==0}
   ]
   
 Hope that helps
 Jens  
  
    


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