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Re: Integrate gives wrong results for a simple polynomial

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  Re: Integrate gives wrong results for a simple polynomial Daniel Lichtblau <danl@wolfram.com> - 2011-04-05 10:42 +0000
    Re: Integrate gives wrong results for a simple polynomial Scott Hemphill <hemphill@hemphills.net> - 2011-04-06 09:13 +0000

#1475 — Re: Integrate gives wrong results for a simple polynomial

Micket 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?

What version? I cannot reproduce it in 8.0.1. I guess I don't even know 
what the "it" is, since you did not indicate what result you obtained. 
[Note to all readers: Don't do that. Nobody likes to guess.]

I also cannot reproduce any problem in previous versions, for the simple 
reason that at the moment I cannot run any such; our machine with those 
caught a cold last week and might be suffering lingering after effects.

So my best guess is this was a bug that, at some point, got fixed.

Daniel Lichtblau
Wolfram Research

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#1501

Daniel Lichtblau <danl@wolfram.com> writes:

> $Assumptions = p > 0; Integrate[Subscript[x, 1]*(1 + y)^2, {y, -1, 1}]

I can confirm that it fails for 7.0.1 under Linux:

In[1]:= $Version

Out[1]= 7.0 for Linux x86 (64-bit) (February 18, 2009)

In[2]:= $Assumptions = p > 0; Integrate[Subscript[x, 1]*(1 + y)^2, {y, -1, 1}]

        x
         1
Out[2]= --
        3

The correct answer should be eight times this value.

Scott
-- 
Scott Hemphill	hemphill@alumni.caltech.edu
"This isn't flying.  This is falling, with style."  -- Buzz Lightyear

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