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Re: Integrate Bug

  • To: mathgroup at smc.vnet.net
  • Subject: [mg100029] Re: Integrate Bug
  • From: Erik Max Francis <max at alcyone.com>
  • Date: Fri, 22 May 2009 01:44:18 -0400 (EDT)
  • References: <gv2jh5$97b$1@smc.vnet.net>

Ney Lemke wrote:
> I am trying to calculate this integral that should be positive.But the
> answer is 0.
> 
> In: Integrate[(1)/(z^2 + b^2 + a^2 - 2 z b Sin[\[Theta]] -
>     2 a b Cos[\[Theta]])^(1/2), {\[Theta], 0, 2 \[Pi]},
>  Assumptions -> {a > 0, b > 0, z > 0}]
> 
> Out:0
> 
> Anybody have notice a situation like that?
> 
> My platform is MacOSX 10.4 and Mathematica 7.

I can confirm that I also get 0 (Mathematica 7.0.1 on CentOS). 
Numerical integrations demonstrate that the result definitely is not 
generally zero for arbitrary positive a, b, and z.  Looks like a bug to me.

-- 
Erik Max Francis && max at alcyone.com && http://www.alcyone.com/max/
  San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M, Skype erikmaxfrancis
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    -- Sandra St. Victor


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