MathGroup Archive 1994

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alternating sums

  • To: mathgroup at
  • Subject: [mg307] alternating sums
  • From: Jack Goldberg <Jack.Goldberg at>
  • Date: Fri, 9 Dec 1994 12:21:07 -0500 (EST)

Here's an elementary question that has me partially stumped.  I often 
have occasion to convert  mylist = {a1,a2,a3,...} into an alternating sum,
a1-a2+a3-a4+... . I find it aesthetically unsatisfactory to generate a 
list of alternating plus and minus ones, multiply mylist with the 
alternating list and then Apply Plus to the product.  It works of course, 
but I have a feeling there is a much better way to do this.  
(This is clearly not of earthshaking importance!!.  I'm just curious.)
Jack Goldberg
Univ of Mich

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