Re: Integrate[ ] returns If[ ] function; how to say it's True?
- To: mathgroup at smc.vnet.net
- Subject: [mg9406] Re: [mg9359] Integrate[ ] returns If[ ] function; how to say it's True?
- From: Daniel Lichtblau <danl>
- Date: Wed, 5 Nov 1997 01:56:26 -0500
- Sender: owner-wri-mathgroup at wolfram.com
AES wrote:
>
> Doing an Integrate[ ] returns an If[condition,a,b] result, with
> complicated expressions for condition, a, and b.
>
> I want to get B as input for the next cell (automatically, not by just
> copying it by hand).
>
> How can I get at the "parts" of the If[ ] statement, or use it in a
> subsequent Input[ ] cell with condition set equal to True?
To get the second element from the If[...] result, one can simply use
Part to extract it:
In[23]:= ee = If[a,b,c]
Out[23]= If[a, b, c]
In[24]:= ee[[2]]
Out[24]= b
One can force Integrate to avoid generation of conditions as below.
Caveat: you may get a result that is only valid for conditions other
than those you have in mind.
In[25]:= Integrate[Cos[a*t^2], {t,-Infinity,Infinity}]
Sqrt[Pi]
Out[25]= If[Im[a] == 0, ---------------,
2 1/4
Sqrt[2] (a )
2
> Integrate[Cos[a t ], {t, -Infinity, Infinity}]]
In[26]:= Integrate[Cos[a*t^2], {t,-Infinity,Infinity},
GenerateConditions->False]
Sqrt[Pi]
Out[26]= ---------------
2 1/4
Sqrt[2] (a )
Daniel Lichtblau
Wolfram Research
danl at wolfram.com