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. > >

**References**:**HoldForm and Sum***From:*dimitris <dimmechan@yahoo.com>