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MathGroup Archive 1997

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Re: Re[a]>0 ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg6241] Re: [mg6198] Re[a]>0 ?
  • From: Mats Jirstrand <matsj at isy.liu.se>
  • Date: Fri, 28 Feb 1997 03:22:27 -0500
  • Organization: Linköping University, Sweden
  • Sender: owner-wri-mathgroup at wolfram.com

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.

Jens,
use the Assumptions option for Integrate!

In[1]:= Integrate[E^(-a*x^2),{x, -Infinity,
Infinity},Assumptions->Re[a]>0]

Out[1]= Sqrt[Pi]/Sqrt[a]

~~~Mats

________________________________________________________

		Mats Jirstrand
     |		Division of Automatic Control
    /|\	   	Dept. of EE, Linkoping University
    \|/	    	S-581 83 Linkoping, Sweden
    /|\		Tel:	+46 13 284042
   / | \   	Fax:	+46 13 282622
 ()  |  ()	Email:	matsj at isy.liu.se
        	WWW:	http://www.control.isy.liu.se


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