       Inconsistent behaviour of Integrate

• To: mathgroup at smc.vnet.net
• Subject: [mg112394] Inconsistent behaviour of Integrate
• From: Andreas Maier <andimai at web.de>
• Date: Tue, 14 Sep 2010 05:12:36 -0400 (EDT)

```Hello,

I'm using Mathematica 7.0.1.0 on Linux x86 (64bit). I have a notebook
file, where I integrate the same integral twice:

In:= Integrate[Sqrt[(x - 1/2)^2 + (y - 1/2)^2], {x, 0, 1}, {y, 0,
1}]
Out= 1/6 (Sqrt + ArcSinh)

In:= Integrate[Sqrt[(x - 1/2)^2 + (y - 1/2)^2], {x, 0, 1}, {y, 0,
1}]
Out= 1/24 (4 Sqrt + Log[17 + 12 Sqrt])

As you can see from the output, integrating the same integral a second
time gives a different result. If I integrate the same integral a
third and a fourth time I always get the second result again. Only if
I restart the mathematica kernel, I get the first result again.
The results are equivalent, since

Log[17 + 12 Sqrt] = Log[(1 + Sqrt)^4] = 4* Log[(1 + Sqrt) = 4* ArcSinh

but somehow Mathematica seems to be able to do this simplification
only once. Is this inconsistent behaviour a bug? Is there a
possibility to give mathematica a hint, so that he always find the
first solution 1/6 (Sqrt + ArcSinh) to the integral?
From

In:= Expand[(1 + Sqrt)^4]
Out= 17 + 12 Sqrt

In:= Factor[%]
Out= 17 + 12 Sqrt

I also figured that Mathematica doesn't seem to be able to factorize
an expression like 17 + 12 Sqrt into (1 + Sqrt)^4. Is this a
known problem? Or should I use a different command to find this
factorization?

Sincerely,
Andreas Maier

```

• Prev by Date: Re: an issue of consistency
• Next by Date: How to rescale the x-axis in an nonlinear way?
• Previous by thread: Re: polynomial long division using Series[] and changing polynomial default
• Next by thread: Re: Inconsistent behaviour of Integrate