Re: "Alternating" function

*To*: mathgroup at smc.vnet.net*Subject*: [mg63269] Re: [mg63260] "Alternating" function*From*: "Ingolf Dahl" <ingolf.dahl at telia.com>*Date*: Thu, 22 Dec 2005 00:04:31 -0500 (EST)*Reply-to*: <ingolf.dahl at telia.com>*Sender*: owner-wri-mathgroup at wolfram.com

Method 1) Differentiate between odd and even numbers, and try the following: g[f_, x_, n_Integer] := If[2*Floor[n/2] == n, Nest[(f[ x + f[x - #]]) &, 0, n/2], (f[x - #]) &@ Nest[(f[x + f[x - #]]) &, 0, (n - 1)/2]] Method 2) With index: g[f_, x_, n_Integer] := Module[{index}, index = 0; Nest[(f[x + (-1)^(index += 1)*#]) &, 0, n]] With both methods, x + g[f, x, 5] gives your function. Best regards Ingolf Dahl Sweden http://web.telia.com/~u31815170/Mathematica/ -----Original Message----- From: Renan [mailto:renan.birck at gmail.com] To: mathgroup at smc.vnet.net Subject: [mg63269] [mg63260] "Alternating" function 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. -- Thanks/obrigado, Renan "Wishmaster" Birck - Canoas, Rio Grande do Sul, Brasil MSN: wizard_of_yendor at hotmail.com Orkut: http://www.orkut.com/Profile.aspx?uid=2202360379963855296