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MathGroup Archive 2005

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Re: Clearing function definitions by argument type?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57247] Re: Clearing function definitions by argument type?
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Sun, 22 May 2005 00:14:11 -0400 (EDT)
  • References: <d6mn17$gkf$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Gareth Russell wrote:
> Hi Group,
> 
> Is there a straightforward way to Clear only definitions that  take 
> certain kinds of arguments? For example, I might have
> 
> f[x_]:=x^2
> f[0]=1
> f[1]=1
> f[2]=7
> ...
> 
> and want to clear all f[number] definitions but not the DelayedSet 
> definition. (Note that the number of f[number] definitions will vary, 
> as will the numbers that each one takes as an argument.)
> 
> My goal is to clear 'memorized' definitions after an optimization run, 
> where the memorized definitions are generated by a
> 
> f[x_]:=f[x]=x^2
> 
> type of function, without clearing the function itself.
> 
> Gareth Russell
> Columbia University
> 
You can see all the assignments in DownValues[g], and you could remove 
the parts of that list that you did not want and then execute 
DownValues[g]:=.....

However, I think it might be easier to rearrange your problem a bit. If 
you 'remember' your answers in another function - g, then you can write 
f as

f[x_] := If[NumberQ[g[x]], g[x], g[x] = x^2]

Then you can just use Clear[g] when you want to start the next problem.

David Bailey
http://www.dbaileyconsultancy.co.uk


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