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
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