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 >