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MathGroup Archive 2007

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Re: Simplification with Integers assumption

  • To: mathgroup at
  • Subject: [mg74897] Re: Simplification with Integers assumption
  • From: "did" <didier.oslo at>
  • Date: Tue, 10 Apr 2007 05:20:00 -0400 (EDT)
  • References: <eunqc2$7ic$><euqnn4$89o$>

On Apr 2, 12:59 pm, "David W.Cantrell" <DWCantr... at> wrote:
> But your post did lead me to find something surprising. Suppose we fix n as
> a positive integer -- say, 3 for example:
> In[6]:= Sum[3/((2p)!(3 - 2p)!), {p, 1, Infinity}]
> results in nothing but warning messages and gibberish. OTOH, if we replace
> Infinity with a large integer -- say, 100 or 1000 -- Mathematica has no
> trouble giving the correct answer.
> In[7]:= Sum[3/((2p)!(3 - 2p)!), {p, 1, 1000}]
> Out[7]= 3/2
> Of course, that answer is _also_ the correct one for the infinite sum at
> which Mathematica balked. Why couldn't Mathematica do the infinite sum? Is
> this problem fixed in the development version perhaps?


Thanks for the reply.
Actually it's not only infinite sums that have problems.
Try, for example,
Sum[3/((2p)!(3 - 2p)!), {p, 1, 10000000000000000000000}]
and you'll get some nonsensical answers too.


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