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MathGroup Archive 1997

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Re: Intelligent handling of Infinity in Limits

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7645] Re: [mg7622] Intelligent handling of Infinity in Limits
  • From: jpk at max.mpae.gwdg.de
  • Date: Tue, 24 Jun 1997 03:36:08 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Peter,

 
> i was trying to do Integrate[ r^2 Exp[-a r^2], {r,0,Infty}]  but MMA
> couldn't simplify a term which clearly was zero.

Look tin "The Book" -- every Mma identifyer is a full (!) english word
starting with a capital, so You have to type Infinity instead of the TeX
abbrevation \infty than all works fine :

In[12]:=
Integrate[ r^2 Exp[-a r^2], {r,0,Infinity}]//InputForm

Out[12]//InputForm=
If[Re[a] > 0, Sqrt[Pi]/(4*a^(3/2)), 
  Integrate[r^2/E^(a*r^2), 
   {r, 0, Infinity}]]


> 
> next i tried integrating over {r,0,r} and then took the limit as r->Infty.
> 

Again Infinity !

Hope that helps
Jens


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