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Re: Extracting a Function's Domain and Image

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67996] Re: Extracting a Function's Domain and Image
  • From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 20 Jul 2006 06:04:39 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <e9ku8v$l1v$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

because Cases[] handels Rules in a special way:
Cases[expr, pattern -> rhs, levspec] gives the 
values of rhs which match the pattern.

and you mean

Cases[h, HoldPattern[f[a_]] -> a, Infinity]

Regards

  Jens

"Bruce Colletti" <vze269bv at verizon.net> schrieb im 
Newsbeitrag news:e9ku8v$l1v$1 at smc.vnet.net...
| Re Mathematica 5.2.2.
|
| Why does the last line of code return {x} and 
not {a,b,_}, while if the f[_]=0 is struck, the 
answer is {a,b}?
|
| I want to extract the domain and image of a 
user-defined function, and tech support 
recommended using DownValues (pretty handy).  If 
you have an easier approach, please share it. 
Thanks.
|
| Bruce
|
| Remove@f;
| f[_]=0;
| f["a"]=1;
| f["b"]=2;
| Clear@x;
| h=DownValues@f
| Cases[h,f[x_]->x,Infinity]
|
| Out[52]=
| {HoldPattern[f[a]]:>1,HoldPattern[f[
|   b]]:>2,HoldPattern[f[_]]:>0}
|
| Out[53]=
| {x}
| 



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