Re: Integrate[ ] returns If[ ] function; how to say it's True?
- To: mathgroup at smc.vnet.net
- Subject: [mg9419] Re: [mg9359] Integrate[ ] returns If[ ] function; how to say it's True?
- From: jpk at max.mpae.gwdg.de
- Date: Wed, 5 Nov 1997 01:56:35 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
> Doing an Integrate[ ] returns an If[condition,a,b] result, with
> complicated expressions for condition, a, and b.
>
Here is an example to avoid the explicit creation of a condition
In[4]:=
Integrate[
Exp[-a*x^2],
{x,-Infinity,Infinity},
Assumptions->{a>0}
] //InputForm
Out[4]//InputForm=
Sqrt[Pi]/Sqrt[a]
> I want to get B as input for the next cell (automatically, not by just
> copying it by hand).
>
In Your If[condition, a, b] ?
In[7]:=
Integrate[Exp[-a*x^2],{x,-Infinity,Infinity}] //InputForm
Out[7]//InputForm=
If[Re[a] > 0,
Sqrt[Pi]/Sqrt[a],
Integrate[E^(-(a*x^2)),
{x, -Infinity, Infinity}]]
This will copy a (with out the condition and the unevaluated integral)
In[8]:=
%[[2]] //InputForm
Out[8]//InputForm=
Sqrt[Pi]/Sqrt[a]
Hope that helps
Jens