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MathGroup Archive 2005

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Re: Quite Upset with NIntegrate

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54172] Re: [mg54142] Quite Upset with NIntegrate
  • From: Chris Chiasson <chris.chiasson at gmail.com>
  • Date: Sat, 12 Feb 2005 01:57:46 -0500 (EST)
  • References: <200502110834.DAA09269@smc.vnet.net>
  • Reply-to: Chris Chiasson <chris.chiasson at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Maybe you should take a small domain of the function and integrate it
numerically. Then feed the same domain into Mathematica and see what
it gets. Depending on the number of dimensions in your integral, you
may want to check the help file to see how Mathematica can be told to
show which points it uses for integration. If you are integrating in
multiple dimensions, perhaps you could evaluate all possible cases of
the integrand and inner integrals first (evaluate them at all points
where they are not close to zero).


On Fri, 11 Feb 2005 03:34:40 -0500 (EST), I. Turan
<ituran at bohr.concordia.ca> wrote:
> Hi:
> 
> I have been trying to evaluate a 4-dimensional integral by using
> NIntegrate with Mathematica 4 w2k.  The integrand and even the
> integration limits are quite complicated (depending on int.
> variables). The length of the integrand is around 2000 lines in the
> FortranForm.
> 
> If I don't play with any options of NIntegrate, It takes one day to
> get one data point and gives very  unreasonably weird values. By
> setting, however, MaxPoints something like 100000 it is possible to
> get faster results but still it seems that Mathematica couldn't handle
> it. When I draw a figure from these data points, it appears very very
> spiky such that it is even not possible to fit the curve. However, it
> is supposed to be very smooth.
> 
> Should I accept that Mathematica can not handle such a
> numerical integration or is there a way to make Nintegrate working
> better?
> 
> Thanks a lot,
> 
> Ismail
> 
> 


-- 
Chris Chiasson
Kettering University
Mechanical Engineering
Graduate Student
1 810 265 3161


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