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MathGroup Archive 2002

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another integral problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32577] another integral problem
  • From: Bradley Stoll <BradleyS at Harker.org>
  • Date: Wed, 30 Jan 2002 03:18:50 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Awhile ago I had a problem with a triple integral.  Now, I've got troubles
with a single integral.  I'm sure that it has something to do with 'how' Mathematica 
finds integrals, but if someone could clue me in...
Integrate[Abs[x^2 Cos[x]-x^3 + x,{x,0,1.1983}] and Integrate[Abs[x^2
Cos[x]-x^3 + x,{x,0,1.19836].  From appearance, you might guess that these
should be pretty close.  The first is pos., while the 2nd is neg, even
though the integrand is non-neg.  FYI, 1.1983 is an approx. to x^2
Cos[x]=x^3 -x.  What's interesting, is that when you use a 'better' approx.,
the result is neg.  Now, with NIntegrate, there is no problem.  Please
advise.

Bradley Stoll


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