Re: Finding length in recursive definition?

*To*: mathgroup at smc.vnet.net*Subject*: [mg60924] Re: Finding length in recursive definition?*From*: "Scout" <mathem at tica.org>*Date*: Tue, 4 Oct 2005 01:24:53 -0400 (EDT)*References*: <dhlcj2$d16$1@smc.vnet.net> <dhntbj$1j9$1@smc.vnet.net> <dhqp87$g8$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Peter, I hope you will accept this simple trick ;-) In[]:= DownValues[f][[-3]]/._[_[_[n_]],r_]:>n ~Scout~ > Scout schrieb: >> Hi Jose, >> If I've well understood your question >> about how many values of a recursive function f[] are stored in memory, >> you can try this: >> >> Length[DownValues[f]] - 1 >> >> where -1 counts the definition of f[] itself. >> >> ~Scout~ >> >> "Jose Reckoner" >> >>>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 >>> >> >> > > Hi ~Scout~, > > what would you do for this function: > > In[1]:= > Clear[f]; > f[1]=1; f[2]=1; > f[n_Integer?EvenQ]:=f[n]=1+f[n/2]; > f[n_]:=f[n]=f[n-1]-1; > > In[5]:= f[17] > Out[5]= 3 > > In[6]:= Definition[f]//InputForm > Out[6]//InputForm= > f[1] = 1 > f[2] = 1 > f[4] = 2 > f[8] = 3 > f[16] = 4 > f[17] = 3 > f[(n_Integer)?EvenQ] := f[n] = 1 + f[n/2] > f[n_] := f[n] = f[n - 1] - 1 > > ? > > Peter >