       Re: Add the Logarithms (error in integral)

• To: mathgroup at smc.vnet.net
• Subject: [mg25157] Re: Add the Logarithms (error in integral)
• From: Jos R Bergervoet <Jos.Bergervoet at philips.com>
• Date: Tue, 12 Sep 2000 02:58:45 -0400 (EDT)
• Organization: Philips Research Laboratories
• References: <8p9j71\$1fl@smc.vnet.net> <KGVu5.30316\$Zh6.36755@ralph.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Jens-Peer Kuska wrote:
>
> h1 = h //. a_.*Log[b_] + c_.*Log[d_] :> Log[b^a*d^c];
>
> Chop[N[h1 /. {a -> 10, b -> 10}]]
>
> 0.000716695

The trick seems interesting. But the answer is incorrect (for
a=b=10 it must be ArcTan[50/Sqrt], which is:

1.3724418046360918933042446254231305679...

-- Jos

> > I'm trying to integrate a function f over a triangle with vertices:
> > (0,0), (a,0), (0,b). My input is:
> >
> >   f = 1/ Sqrt[1+x^2+y^2]^3
> >   g = Integrate[f, {y,0, b-b x/a} ]
> >   h = Integrate[g, {x,0,a}]
> >   N[ h /. {a->10, b->10} ]
> >
> > With a=b=10, the output for this positive(!) function is negative:
> >
> >   Out= -4.91074 + 0. I
> >
> > which is obviously wrong.

```

• Prev by Date: Re: Syntax Error in .nb File
• Next by Date: Re: Evaluate a string