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MathGroup Archive 2005

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Re: "Alternating" function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63274] Re: [mg63260] "Alternating" function
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Thu, 22 Dec 2005 00:04:35 -0500 (EST)
  • References: <200512210435.XAA14743@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On Dec 20, 2005, at 11:35 PM, Renan wrote:

> Hello,
>
> I want to make a "nested function" like: x + f[x - f[x + f[x - f[x  
> + f[x]]]]].
>
> I've tried using Nest but I don't find how to keep switching between
> Plus and Minus: I would need something that would return an "index" so
> I could keep track of when I need to "switch" the operation. (e.g. if
> the "index" is odd, the operation is "Plus", otherwise is "Minus")
>
> How can I make this? I looked in the help but didn't find any  
> informations.
>
> Thanks.

One way is to use Fold instead of Nest

Fold[x+#2 f[#1]&,x,Table[(-1)^i,{i,0,n-1}]

where n in is the desired level of nesting.

Regards,

Ssezi


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