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Re: Differences between recursions and limit

• To: mathgroup at smc.vnet.net
• Subject: [mg60551] Re: Differences between recursions and limit
• From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
• Date: Tue, 20 Sep 2005 05:19:06 -0400 (EDT)
• Organization: Uni Leipzig
• References: <dgm01k$njm$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

look in the manual about dynamic programming
and change your definition to

x[0]=0;
x[k_] :=x[k]= .25 *(1 + x[k-1] + (x[k-1])^2 + 
(x[k-1])^3);

Regards
  Jens

"anbra1" <xyxanbra1 at tiscalixxxyxxx.it> schrieb im 
Newsbeitrag news:dgm01k$njm$1 at smc.vnet.net...
| Please,
| I want to know
| why these two recursions,doing the same thing,
| are the first one much more slow than the second
|
| -------------------------
|
| x[0]=0;
| x[k_] := .25 *(1 + x[k-1] + (x[k-1])^2 + 
(x[k-1])^3);
|
| For[k=1,k<12,Print[k," 
",SetPrecision[x[k],30]];k++]
|
| -------------------------
|
| a=0;
|
| For[k=1,k<12,k++,
|
| b= .25 (1 + a + a^2 + a^3);a:=b;Print[k," 
",SetPrecision[b,30]]]
|
| -------------------------
| Another question
| How can I calculate
| the limit of this recursion for k->Infinite ?
| Thank you all
|
|