memoizing function again

*To*: mathgroup at smc.vnet.net*Subject*: [mg32495] memoizing function again*From*: Erich Neuwirth <erich.neuwirth at univie.ac.at>*Date*: Wed, 23 Jan 2002 01:00:22 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

i have the following function f[x_] /; x <= 2 := f[x] = 1 f[x_] /; x > 2 := f[x] = f[x - 1] + f[x - 2] it remembers what it already calculated i want to be able to throw away rules with values between calculations In[3]=DownValues[f] produces Out[3]={HoldPattern[f[x_]/;x\[LessEqual]2]\[RuleDelayed](f[x]=1), HoldPattern[f[x_]/;x>2]\[RuleDelayed](f[x]=f[x-1]+f[x-2])} after f[4] we have In[5]:= DownValues[f] Out[5]= {HoldPattern[f[1]]\[RuleDelayed]1,HoldPattern[f[2]]\[RuleDelayed]1, HoldPattern[f[3]]\[RuleDelayed]2,HoldPattern[f[4]]\[RuleDelayed]3, HoldPattern[f[x_]/;x\[LessEqual]2]\[RuleDelayed](f[x]=1), HoldPattern[f[x_]/;x>2]\[RuleDelayed](f[x]=f[x-1]+f[x-2])} \[RuleDelayed] is ascii for :>, i think so DownValues[f] = Take[DownValues[f], -2] removes all the rules giving calculated values but i would like to throw away the rules following the pattern HoldPattern[f[x_Integer]:>y_Integer but i have not been able wo write an expression using Cases and a pattern which gets rid of the rules i want to get rid of -- Erich Neuwirth, Computer Supported Didactics Working Group Visit our SunSITE at http://sunsite.univie.ac.at Phone: +43-1-4277-38624 Fax: +43-1-4277-9386