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MathGroup Archive 2005

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Re: Finding length in recursive definition?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg60887] Re: [mg60877] Finding length in recursive definition?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 2 Oct 2005 01:54:39 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

Clear[f]

f[1]=1;
f[2]=3;
f[n_]:=f[n]=f[n-1]+f[n-2];


f[3]

4

Max[Cases[ReleaseHold[(First/@DownValues[f])/.
        HoldPattern[f[n_]]:>n],_Integer]]

3

or more simply

Length[DownValues[f]]-1

3


Bob Hanlon

> 
> From: "Jose  Reckoner" <reckoner at gmail.com>
To: mathgroup at smc.vnet.net
> Date: 2005/10/01 Sat AM 02:55:52 EDT
> Subject: [mg60887] [mg60877] Finding length in recursive definition?
> 
> I have something like:
> f[1] = 1
> f[2] = 3
> f[n_] := f[n] = f[n - 1] + f[n - 2]
> 
> and in the course of work, f[n] gets evaluated an unknown number of
> times resulting in
> 
> >> ?f
> f[1] = 1
> f[2] = 3
> f[3] = 4
> f[n_] := f[n] = f[n - 1] + f[n - 2]
> 
> I want to figure out the greatest integer n such that f[n] has already
> been computed and is stored. In this case, it is 3.
> 
> How can I do this?
> 
> Thanks!
> 
> Jose
> 
> 


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