MathGroup Archive 1994

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Alternating Sums

  • To: mathgroup at
  • Subject: [mg340] Alternating Sums
  • From: Xah Y Lee <xyl10060 at>
  • Date: Mon, 19 Dec 1994 07:06:27 -0800 (PST)

This message is supposed to go to Jack Goldberg. I lost his email address.

Subject: Ways to construct alternating sums in mma.

Hi Jack. You may find the following code to construct mylist useful for 
testing purposes.

mylist =
            ToExpression@StringJoin["a", ToString[i]], {i,1 , 12 }

I think the simplist is

 - Sum[ (-1)^i mylist[[i]], {i,1, Length[mylist]} ]

I made a study of all the contributions so far. I am amazed that the one 
using Fold is fastest.

 Xah Lee
 xyl10060 at
 Mountain View, CA.

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