Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2000
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2000

[Date Index] [Thread Index] [Author Index]

Search the Archive

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[101]], 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]= -4.91074 + 0. I
> >
> > which is obviously wrong.


  • Prev by Date: Re: Syntax Error in .nb File
  • Next by Date: Re: Evaluate a string
  • Previous by thread: Re: Add the Logarithms (error in integral)
  • Next by thread: Re: Add the Logarithms (error in integral)