Re: Integrate Bug

*To*: mathgroup at smc.vnet.net*Subject*: [mg100673] Re: Integrate Bug*From*: Valeri Astanoff <astanoff at gmail.com>*Date*: Wed, 10 Jun 2009 17:13:01 -0400 (EDT)*References*: <gv2jh5$97b$1@smc.vnet.net>

On 21 mai, 05:58, Ney Lemke <ney.nle... at gmail.com> 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. > > Best wishes, Good day, Here is the most compact form of the integral, due to Dr. Andreas Dieckmann, who e-mailed me he used "transformations (17.4.3), (17.4.11) and (17.4.15) given in Abramowitz/Stegun" : 4*EllipticK[(4*b*Sqrt[a^2 + z^2])/(b + Sqrt[a^2 + z^2])^2]/(b + Sqrt [a^2 + z^2]) -- Valeri Astanoff p.s. I'm a bit disappointed FullSimplify couldn't do the same...