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.
> 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
>

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

```

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