Re: Mathematica 8 does not like Sum[1/k,{k,n,10}]

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• Subject: [mg130771] Re: Mathematica 8 does not like Sum[1/k,{k,n,10}]
• From: Bob Hanlon <hanlonr357 at gmail.com>
• Date: Mon, 13 May 2013 03:48:43 -0400 (EDT)
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```Without giving n a specific value in your definition, Mathematica has no
way of knowing that you intend n to be an integer in the range [1, 8].

\$Version

"8.0 for Mac OS X x86 (64-bit) (October 5, 2011)"

f1[n_Integer?(0 < # < 9 &)] :=
Sum[1/k, {k, n, 8}]

f2[n_Integer?(0 < # < 9 &)] :=
Sum[1/k, {k, 8, n, -1}]

Table[f1[n] == f2[n] == Sum[1/k, {k, n, 8}], {n, 0, 9}] // Quiet

{f1[0] == f2[0] ==
ComplexInfinity, True, True, True, True, True, True, True, True,
f1[9] == f2[9] == 0}

Bob Hanlon

On Sun, May 12, 2013 at 3:29 AM, valvola <g.resta at iit.cnr.it> wrote:

> Apparently, Mathematica 8 does not like the simple expression:
>
> Clear[k,n]; Sum[1/k,{k,n,8}]
>
> The result is two errors:
> Power::infy: "Infinite expression 1/0 encountered."
>
> and a large expression
> DifferenceRoot[
>  Function[{\[FormalY], \[FormalN]}, {\[FormalN] \
> \[FormalY][\[FormalN]] + .... etc.etc.
>
> By the way, the similar Sum[1/k, {k, 8, n}] works fine.
>
> ????
> g.
>
>

```

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