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Re: pretty output with HoldForm

• To: mathgroup at smc.vnet.net
• Subject: [mg70483] Re: pretty output with HoldForm
• From: dimmechan at yahoo.com
• Date: Tue, 17 Oct 2006 02:59:31 -0400 (EDT)
• References: <egva7f$rgs$1@smc.vnet.net>

One method is to use the defined function EvaluateAt, which you can
find it in the
Further Examples of ReplacePart at the Help Browser or at

http://documents.wolfram.com/mathematica/Built-inFunctions/ListsAndMatrices/ListOperations/FurtherExamples/ReplacePart.html

See also

http://www.verbeia.com/mathematica/tips/HTMLLinks/Tricks_Misc_1.html
http://library.wolfram.com/infocenter/MathSource/495/

In what follows everything is in InputForm

Here is the definition of EvaluateAt

EvaluateAt[expr_, positions_] := Fold[ReplacePart[#1, #1[[Sequence @@
#2]], #2] & ,
expr, positions]

Here is your function, as a pure function

f = HoldForm[1/(2*#1 + 1) - 1/(4*#1 + 2) - 1/(4*#1 + 4)] & ;

Here is the sum

Sum[f[i], {i, 1, 5}]
HoldForm[1/(2*1 + 1) - 1/(4*1 + 2) - 1/(4*1 + 4)] + HoldForm[1/(2*2 +
1) - 1/(4*2 + 2) -
1/(4*2 + 4)] + HoldForm[1/(2*3 + 1) - 1/(4*3 + 2) - 1/(4*3 + 4)] +
HoldForm[1/(2*4 + 1) -
 1/(4*4 + 2) - 1/(4*4 + 4)] + HoldForm[1/(2*5 + 1) - 1/(4*5 + 2) -
1/(4*5 + 4)]

And here is the sum in the desired format

EvaluateAt[%, Position[%, _Times]]
HoldForm[1/3 - 1/6 - 1/8] + HoldForm[1/5 - 1/10 - 1/12] + HoldForm[1/7
- 1/14 - 1/16] + HoldForm[1/9 - 1/18 - 1/20] +  HoldForm[1/11 - 1/22 -
1/24]

Regards
Dimitris