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Re: Generalization of Variables ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109242] Re: Generalization of Variables ?
  • From: Yves Klett <yves.klett at googlemail.com>
  • Date: Mon, 19 Apr 2010 02:48:11 -0400 (EDT)
  • References: <hqc14l$g2v$1@smc.vnet.net>

Hi Jack,

your pasted code seems incomplete. On short notice, perhaps something like

vars[expr_] :=
 Union[Cases[expr, s_Symbol /; Not[NumericQ[s]], Infinity]]

vars[Sin[x] + Exp[x^2 + b + Cos[t]] + \[Pi]]
{b, t, x}

might help as well. This one also eliminates symbols that have a
numerical counterpart.

Regards,
Yves

Am 17.04.2010 12:05, schrieb Jack L Goldberg 1:
> Hi Folks,
> 
> The built-in command "Variables" does not give the (naively expected)  
> answer when it is called with functions such as x + Sin[x].  This  
> behavior is mentioned in the description of "Variables".
> I have constructed a generalization of "Variables" which works as  
> expected - I think?  I would appreciated a critique of this code which  
> addresses these issues:
> 
> a) Is there a situation in which it fails?
> 
> b) If the code works, can it be improved.
> 
> Question b) is asked because I am not fully acquainted with all of  
> Mathematica's commands.
> 
> Here is the code.
> 
> variables[f_]:= Flatten[
>                         Union[
>                              Cases[
>                                     Map[N,Level[f,{-1},z_Symbol]]/.True->{}
>                                             ]
> 
> I have tried "variables" on functions coded in the obvious manner, say,
> Sin[x]+Exp[x^2],  Sin[x+y]-z^2, etc. and a few esoteric examples.
> 
> Jack
> 


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