Re: Extracting a Function's Domain and Image
- To: mathgroup at smc.vnet.net
- Subject: [mg67987] Re: Extracting a Function's Domain and Image
- From: Peter Pein <petsie at dordos.net>
- Date: Thu, 20 Jul 2006 06:04:22 -0400 (EDT)
- References: <e9ku8v$l1v$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Bruce Colletti schrieb:
> 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}
>
Cases[h,HoldPattern[f[x_]]->x,Infinity]
--> {a,b,_}
... or did I misunderstand you?
Peter