RE: another integral problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg32613] RE: [mg32577] another integral problem*From*: Bradley Stoll <BradleyS at Harker.org>*Date*: Thu, 31 Jan 2002 01:45:47 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Although that was an error on my part (please close off the absolute value argument with a ]), that was not the problem. Thanks for catching that, Dave. I should do as I suggest my students do, cut and paste instead of retyping. Bradley -----Original Message----- From: David Terr [mailto:dterr at wolfram.com] To: mathgroup at smc.vnet.net Subject: [mg32613] Re: [mg32577] another integral problem Bradley Stoll wrote: > 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 It looks like you put the brackets for Abs in the wrong place - the closing bracket should go after the last x. David Mathematica 5.0 for Linux Copyright 1988-2001 Wolfram Research, Inc. -- Motif graphics initialized -- In[1]:= Integrate[Abs[x^2 Cos[x]-x^3+x],{x,0,1.1983}] Out[1]= 0.549322 In[2]:= Integrate[Abs[x^2 Cos[x]-x^3+x],{x,0,1.19836}] Out[2]= 0.549322