Re: Integrate gives wrong results for a simple polynomial
- To: mathgroup at smc.vnet.net
- Subject: [mg117946] Re: Integrate gives wrong results for a simple polynomial
- From: Mikael Ãhman <micketeer at gmail.com>
- Date: Tue, 5 Apr 2011 06:43:56 -0400 (EDT)
Thank you for your reply. I tried some other computers around the office. Everyone with 8.0 got it right, but my computer and another windows computer with version 7 gets the wrong answer (off by a factor 8) Some variations of the integral, like ^3 or more also yields the incorrect answer. {$Version, $ReleaseNumber} {"7.0 for Linux x86 (64-bit) (February 18, 2009)", 1} $Assumptions = p > 0; Integrate[Subscript[x, 1]*(1 + y)^2, {y, -1, 1}] Subscript[x, 1]/3 $Assumptions = p > 0; Integrate[x*(1 + y)^2, {y, -1, 1}] (8 x)/3 $Assumptions = True; Integrate[Subscript[x, 1]*(1 + y)^2, {y, -1, 1}] (8 Subscript[x, 1])/3 On Mon, Apr 4, 2011 at 2:11 PM, Bob Hanlon <hanlonr at cox.net> wrote: > > Appears to work fine here. What result did you get and with which system and version. > > {$Version, $ReleaseNumber} > > {"8.0 for Mac OS X x86 (64-bit) (February 23, 2011)", 1} > > $Assumptions = p > 0; Integrate[Subscript[x, 1]*(1 + y)^2, {y, -1, 1}] > > (8*Subscript[x, 1])/3 > > $Assumptions = p > 0; Integrate[x*(1 + y)^2, {y, -1, 1}] > > (8*x)/3 > > $Assumptions = True; Integrate[Subscript[x, 1]*(1 + y)^2, {y, -1, 1}] > > (8*Subscript[x, 1])/3 > > Integrate[(1 + y)^2, {y, -1, 1}] > > 8/3 > > > Bob Hanlon > > ---- Micket <micketeer at gmail.com> wrote: > > ============= > I have had the bad luck to discover a strange bug (?) when computing > some integrals with mathematica. > I simplified it as far as i could; > $Assumptions = p > 0; Integrate[Subscript[x, 1]*(1 + y)^2, {y, -1, 1}] > > If i change anything else, be it the assumption (yes, it is a > completely unrelated variable), the subscript, the integration limits, > the exponent, the addition, it works out the correct answer. > > It also takes a significant time (a few seconds) to compute this > integral. > > Does anyone have an explanation for this behavior? > >