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Re: Symbols in expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg89131] Re: Symbols in expression
  • From: sigmundv at gmail.com
  • Date: Mon, 26 May 2008 06:23:58 -0400 (EDT)
  • References: <g1dhtv$9m1$1@smc.vnet.net>

Thank you, Bob, but isn't

Union[Cases[r, _?(Head[#] == Symbol && ! NumericQ[#] &), Infinity]]

equivalent to

Union[Cases[r, _Symbol?(! NumericQ[#] &), Infinity]] ?

/Sigmund


On May 26, 7:30 am, Bob Hanlon <hanl... at cox.net> wrote:
> 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
>
>
>
> ---- sigmu... 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



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