Re: Symbols in expression

*To*: mathgroup at smc.vnet.net*Subject*: [mg89098] Re: Symbols in expression*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sun, 25 May 2008 06:27:24 -0400 (EDT)*References*: <200805250722.DAA18957@smc.vnet.net>

On 25 May 2008, at 16:22, 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 > Your question is far from clear, but this pehraps might be what you are lookign for: r = {Cos[u] Sin[v], Sin[u] Sin[v], Cos[v]}; Union[Cases[r, _Symbol?(Not[NumericQ[#]] &), {-1}]] {u, v} The Not[NumericQ[#]] & part is needed in case you r was something like: r = {Cos[2Pi u] Sin[2Pi v], Sin[2Pi u] Sin[2Pi v], Cos[2 Pi v]}; Andrzej Kozlowski

**References**:**Symbols in expression***From:*sigmundv@gmail.com