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MathGroup Archive 2006

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Re: Product and Summation sign

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66814] Re: Product and Summation sign
  • From: "Steve Luttrell" <steve_usenet at _removemefirst_luttrell.org.uk>
  • Date: Wed, 31 May 2006 06:31:15 -0400 (EDT)
  • References: <e5h5d7$eo7$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

?Sum

gives

"Sum[f, {i, imax}] evaluates the sum of the expressions f as evaluated for 
each i from 1 to imax. Sum[f, {i, imin, imax}] starts with i = imin. Sum[f, 
{i, imin, imax, di}] uses steps di. Sum[f, {i, imin, imax}, {j, jmin, jmax}, 
... ] evaluates a sum over multiple indices."

so the result that you obtained from Sum[x[i],{i,1,50}] was the correctly 
evaluated result.

However

?HoldForm

gives

"HoldForm[expr] prints as the expression expr, with expr maintained in an 
unevaluated form."

so to obtain the result that you wanted to see (i.e. one that is 
unevaluated) then you need to to evaluate

Sum[x[i],{i,1,50}]//HoldForm

Steve Luttrell
West Malvern, UK

<actuary at mchsi.com> wrote in message news:e5h5d7$eo7$1 at smc.vnet.net...
> While a Mathematica user for some time,  use has been limited to number
> crunching and not symbolic manipulations.  I started to remedy this
> over the weekend.
>
> I entered Sum[x[i],{i,1,50}] expecting to see a response with Summation
> sign.  Instead the output was x[1}+x[2]+x[3]+.....
>
> What do I need to do to get output that includes the Summation sign?
> StandardForm was checked.
>
> Thanks.
>
> Larry
> 



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