Re: Re: Defining Real Expressions

*To*: mathgroup at smc.vnet.net*Subject*: [mg8597] Re: [mg8535] Re: Defining Real Expressions*From*: jpk at max.mpae.gwdg.de*Date*: Tue, 9 Sep 1997 03:07:15 -0400*Sender*: owner-wri-mathgroup at wolfram.com

> 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