Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1999
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1999

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Question about evaluation with Sum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19602] Re: [mg19587] Question about evaluation with Sum
  • From: "Andrzej Kozlowski" <andrzej at tuins.ac.jp>
  • Date: Sat, 4 Sep 1999 21:09:12 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

This has already been discussed here and is undoubtedly caused a bug in Sum
(whatever anyone might tell you about the role of Attributes here). The best
way to see it  is (in my opinion) by contrasting it with the behaviour of
Product, which has exactly the same Attributes as Sum:

In[1]:=
p=k
Out[1]=
k
In[2]:=
Product[p,{k, 1, n}]
Out[2]=
n!

In[3]:=
Product[Evaluate[p],{k, 1, n}]
Out[3]=
n!

(I hope that  wri does not decide that there is a bug in Product!)
--
Andrzej Kozlowski
Toyama International University
JAPAN
http://sigma.tuins.ac.jp
http://eri2.tuins.ac.jp


----------
>From: CORNIL Jack Michel <jmcornil at club-internet.fr>
To: mathgroup at smc.vnet.net
>To: mathgroup at smc.vnet.net
>Subject: [mg19602] [mg19587] Question about evaluation with Sum
>Date: Sat, Sep 4, 1999, 2:34 PM
>

> Hello,
>
>
> I have a big problem of evaluation with the function Sum.
>
> With the very simple following example,
>
>    p=k
>
>    Sum[p,{k, 1, n}]
>
>      p k
>
>    Sum[Evaluate[p], {k, 1, n}]
>
>      1
>      - n (1+n)
>      2
>
>    Sum[p,{k, 1, 5}]
>
>      15
>
> how can I explain my students that
>
>    in the first case p is left unevaluate and it needs Evaluate,
>
>    in the last case p is evaluate correctly  ?
>
> I do not understand how the "Attributes" of Sum can explain this.
>
>
> Thank You in advance
>
>
> Jack Michel CORNIL
>
> Versailles FRANCE
>
> 


  • Prev by Date: Re: Help: Outer of a list of lists
  • Next by Date: Re: Element extraction
  • Previous by thread: Re: Question about evaluation with Sum
  • Next by thread: Re: Question about evaluation with Sum