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MathGroup Archive 2004

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Re: Question about Integrate and If

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46649] Re: Question about Integrate and If
  • From: phbrf at t-online.de (Peter Breitfeld)
  • Date: Thu, 26 Feb 2004 17:53:56 -0500 (EST)
  • References: <c1iqub$69a$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Antonio González <SPAMgonferNO at esi.us.es> wrote:

> Setting the trivial integral
> 
> Integrate[1/x,{x,a,2a}]
[*snip*]

> 
> Integrate[1/x, {x, a, 2*a}, Assumptions -> a != 0]
> 
> the result is
> 
> If[Im[a] != 0 || Re[a] != 0, Log[2], Integrate[x^(-1), {x, a, 2*a},
>   Assumptions -> a != 0 && Im[a] == 0 && Re[a] == 0]]
> 
> that is even worse, as if I assume that a!=0, it is
> obvious that Im[a] != 0 || Re[a] != 0 (how could it be
> that a != 0 && Im[a] == 0 && Re[a] == 0 ?)
> 
> Can anybody explain this strange behavior? Why does not give
> the answer
> 
> If[a!= 0, Log[2],Indeterminate]
> 
> or something like that?
> 
>   Antonio

That's really strange, but the Assumption->{a<0||a>0} gives the right
result.

-- 
Gruß Peter
-- 
==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==
Peter Breitfeld, Bad Saulgau, Germany  -- <http://www.pBreitfeld.de>


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