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MathGroup Archive 2007

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Re: A wrong definite integral in 5.0?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77229] Re: A wrong definite integral in 5.0?
  • From: Valeri Astanoff <astanoff at gmail.com>
  • Date: Wed, 6 Jun 2007 06:45:12 -0400 (EDT)
  • References: <f43hau$301$1@smc.vnet.net>

On 5 juin, 13:27, bolud-el-kotur <ke8e... at hotmail.com> wrote:
> I get this result in version 5.0,
>
> >Integrate[Log[1 - 4 x(1 - x)], {x, 0, 1}]
> >-2 + I  Pi
>
> and the same thing if I "declare" the singularity with {x,0,1/2,1}.
>
> Another way to look at the problem is computing,
>
> >Integrate[Log[1 - 4 x(1 - x)], {x, 0, 1/2}]
> >-1
>
> and
>
> >Integrate[Log[1 - 4 x(1 - x)], {x, 1/2, 1}]
> >-1 + I Pi
>
> Since the integrand is symmetric about x=1/2, the result should have
> been the same one (-1) in both cases, and the integral over [0,1]
> should yield -2.
>
> A numerical approach,
>
> >NIntegrate[Log[1 - 4 x(1 - x)], {x, 0, 1/2, 1},
>
>   MaxRecursion -> 100, SingularityDepth -> 20]
>
> >-1.9999997086422834`
>
> gives the correct result, within the numerical accuracy required.

Good day,

It was corrected in version 5.1 :

In[1]:= Integrate[Log[1-4 x(1-x)],{x,0,1}]
Out[1]=-2

In[2]:=$Version
Out[2]=5.1 for Microsoft Windows (January 28, 2005)


V.Astanoff



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