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
• 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
/|\		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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