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MathGroup Archive 1997

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Re: Re[a]>0 ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg6227] Re: [mg6198] Re[a]>0 ?
  • From: "w.meeussen" <w.meeussen at solair4b.eunet.be>
  • Date: Fri, 28 Feb 1997 03:21:48 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

At 02:53 27-02-97 -0500, Jens Dreger wrote:
>Hi !
>
>Can anyone tell me how I can make MMA take Re[a] for greater than 0 ?
>
>
>In[1]:= Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]
>
>Out[1]:= If[Re[a] > 0, Sqrt[Pi]/Sqrt[a], 
>          Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]]
>
>I would like to have just the answer "Sqrt[Pi]/Sqrt[a]", since I know
>that Re[a]>0 is true.
>
>BTW: a/:Re[a]=1 works, but I don't want to specify the real part of a,
>just want to say it's greater than zero.
>
>Thanks !
>
>Jens.
>
>
>
hi Jens,

either after evaluation:

In[5]:=
Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]
Out[5]=
If[Re[a] > 0, Sqrt[Pi]/Sqrt[a], 
  Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]]

In[6]:=
% /. Re[a] > 0 -> True
Out[6]=
Sqrt[Pi]/Sqrt[a]

or better yet, before it:

In[30]:=
Integrate[E^(-a*x^2), {x, -Infinity, Infinity}, 
  Assumptions -> {Re[a] > 0}]
Out[30]=
Sqrt[Pi]/Sqrt[a]

all the best,

Dr. Wouter L. J. MEEUSSEN
w.meeussen at solair4b.eunet.be



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