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Re: HoldForm and Sum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg121793] Re: HoldForm and Sum
  • From: "Tong Shiu-sing" <sstong at phy.cuhk.edu.hk>
  • Date: Mon, 3 Oct 2011 04:19:55 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201110010707.DAA17769@smc.vnet.net>

Hello,

You can change the attributes of Plus to achieve the forms:
Unprotect[Plus]
ClearAttributes[Plus, Orderless]

Sum[(HoldForm[#1] &)[1/i], {i, 1, 10}]
gives
1+1/2+1/3...+1/8+1/9+1/10

Sum[((-1)^Quotient[i - 1, 3] HoldForm[#1] &)[1/i], {i, 1, 12}]
gives
1+1/2+1/3-1/4-1/5-1/6+1/7+1/8+1/9-1/10-1/11-1/12

Hope this is useful. 

Regards,
Dominic

----- Original Message ----- 
From: "dimitris" <dimmechan at yahoo.com>
To: <mathgroup at smc.vnet.net>
Sent: Saturday, October 01, 2011 3:07 PM
Subject: [mg121793] HoldForm and Sum


> Hell to all.
> 
> A (well-known) nice example of the use of HoldForm is:
> 
> Sum[(HoldForm[#1] & )[i], {i, 1, 10}]
> 
> (*output omited*)
> 
> I want to do the same with 1/i
> 
> Sum[(HoldForm[#1] & )[1/i], {i, 1, 10}]
> 
> Mathematica output is
> 
> 1/10+1/9+1/8+...+1/3+1/2+1
> 
> My first question is how can I get the output in the form
> 
> 1+1/2+1/3...+1/8+1/9+1/10
> 
> 
> My second query comes now. How can I combine HoldForm and Sum (or
> anything else) in order to have the following output (unevaluated)?
> 
> 1+1/2+1/3-1/4-1/5-1/6+1/7+1/8+1/9-1/10-1/11-1/12
> 
> that is, three positive terms after three negative and so on.
> 
> Thank you in advance for your response.
> 
>



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