Re: alternating sums
- To: mathgroup at christensen.Cybernetics.NET
- Subject: [mg334] Re: [mg307] alternating sums
- From: Ross Moore <ross at zeus.mpce.mq.edu.au>
- Date: Fri, 16 Dec 94 15:37:48 +1100
Lots of people have responded to this one ...
>> stumped. I often have occasion to convert mylist =
>> {a1,a2,a3,...} into an alternating sum, a1-a2+a3-a4+...
> Jack,
>
> Here's the best I could do off the top of my head. I suspect there's
> something simpler still, but...
... so my contribution is illustrative of a more general technique:
mylist = {a1,a2,a3,a4,a5,a6};
sgn=-1; Plus@@((sgn *=-1;sgn #)&/@ mylist )
(zeus) Out[17]=
a1 - a2 + a3 - a4 + a5 - a6
Regards,
Ross Moore
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Ross Moore Internet: ross at mpce.mq.edu.au
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