Re: Symbols in expression
- To: mathgroup at smc.vnet.net
- Subject: [mg89106] Re: [mg89079] Symbols in expression
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Mon, 26 May 2008 01:28:27 -0400 (EDT)
- Reply-to: hanlonr at cox.net
r = {Cos[u] Sin[v], Sin[u] Sin[v], Cos[v]};
Union[Cases[r, _Symbol, Infinity]]
{u,v}
However, this will include numbers if there are numeric symbols such as Pi or E present. Hence, use
Union[Cases[r, _?(Head[#] == Symbol && ! NumericQ[#] &), Infinity]]
{u,v}
Bob Hanlon
---- sigmundv at gmail.com wrote:
> Dear all,
>
> Define, say,
>
> r = {Cos[u] Sin[v],Sin[u] Sin[v],Cos[v]}.
>
> How can I write a function, which takes r as an argument and returns a
> list {u,v}? If we defined r[u_,v_]:=... it could be achieved fairly
> easily using DownValues. But how can I achieve it in this case?
>
> Kind regards,
> Sigmund Vestergaard
>