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Re: Bug in Sum?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg119971] Re: Bug in Sum?
  • From: Dana DeLouis <dana01 at me.com>
  • Date: Sat, 2 Jul 2011 05:02:21 -0400 (EDT)

Hi.  I've noticed over time that Mathematica doesn't work well with specific values in the power function, just as you noticed.
It's been this way for a while.
I find that using a variable for the power usually works well.
Hence...

Sum[1/((n*(1 + n))*(1 - x)^p), {n, 1, m}]

m/((1 - x)^p*(1 + m))

Then... put your power of 4 back in:

% /. p -> 4
m/((1 + m)*(1 - x)^4)

Just note that the capital letter M is a reserve word in the Combinatorica Package.

= = = = = = = = = =
HTH  : >)
Dana DeLouis
$Version
8.0 for Mac OS X x86 (64-bit) (November 6, 2010)



On Jun 29, 5:42 pm, Dario <dario.benede... 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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