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Re: Bug in Sum?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg119939] Re: Bug in Sum?
  • From: Phil J Taylor <xptaylor at gmail.com>
  • Date: Thu, 30 Jun 2011 20:40:03 -0400 (EDT)
  • References: <201106301029.GAA15424@smc.vnet.net>

Works in version 6.0

In[1]:= Sum[1/(n (1 + n)) 1/((1 - x)^4), {n, 1, M}]
$Version

Out[1]= M/((1 + M) (1 - x)^4)

Out[2]= "6.0 for Microsoft Windows (32-bit) (June 19, 2007)"

On Thu, Jun 30, 2011 at 6:29 AM, Bob Hanlon <hanlonr at cox.net> wrote:

>
> For a workaround, generalize the problem
>
> Sum[1/(n (1 + n)) 1/((1 - x)^r), {n, 1, M}]
>
> M/((1 - x)^r*(1 + M))
>
> % /. r -> 4
>
> M/((1 + M)*(1 - x)^4)
>
>
> Bob Hanlon
>
> ---- Dario <dario.benedetti at aei.mpg.de> wrote:
>
> =============
> I am very puzzled by the fact that Mathematica does not evaluate the
> following Sum (it keeps running endlessly):
>
> Sum[1/(n  (1 + n)) 1/((1 - x)^4) , {n, 1, M}]
>
> where x and M are some undefined variables,
>
> but it does evaluate
>
> Sum[1/(n  (1 + n)) 1/((1 - x)^2) , {n, 1, M}]
>
> where I have only changed the power of (1-x), which should not matter as it
> must factor out!
>
> Any help on this please?
>
>
>
>


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