Re: help: recursive functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg32620] Re: help: recursive functions*From*: Erk Jensen <Erk.Jensen at cern.ch>*Date*: Fri, 1 Feb 2002 02:02:21 -0500 (EST)*References*: <a3aqpd$4cv$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Okke wrote: > > Hello, > > I'm having some problems with a recursive function. > Could somebody please help me by telling me how I > should enter such a function? > > tia, > > This is what I've done so far: > > f[n_]:=Sin[Pi*n*(0.05+(0.0005*n))] > y[n_]:=1.5*y[n-1]-0.85*y[n-2]+f[n] > > I'm trying to Plot[y[n],{n,0,320}] but that gives me > an error: $RecursionLimit::reclim: Recursion depth of 256 exceeded. > > btw, is there an option to fill the area under the sine? > > -- > Okke > > remove NOSPAM from my email address to reply You should at least define y[n_ /; n < 0], otherwise the recursion will of course be infinite. In your example, at n=0 for example Mathematica will try to evaluate. Using your formula, it will have to evaluate at n=-1 and n=-2. For these, it will try to evaluate at n=-4, -3, and again -2. For these, it ... and so on - no recursion limit! Mathematica gives up after $RecursionLimit. Ciao -erk- -- Dr.-Ing. Erk JENSEN mailto:Erk.Jensen at cern.ch CERN PS/RF L19510 http://cern.ch/Erk.Jensen CH-1211 Geneva 23 Tel.: +41 22 76 74298 Switzerland Fax.: +41 22 76 78510