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MathGroup Archive 2001

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Re: What variables are in a function and displaying surds

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31133] Re: What variables are in a function and displaying surds
  • From: Albert Retey <albert.retey at visualanalysis.com>
  • Date: Fri, 12 Oct 2001 03:36:52 -0400 (EDT)
  • Organization: Visual Analysis AG
  • References: <9q2l3v$p4f$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

> Is there a way in Mathematica to generate a list of variables in an
> expression like Variable[]. For example if I passed the expression
> Sin[x+y]+ z/p - t the list {x,y,z,p,t} would be generated.
> 

This is probably not bullet-proof, but should do the job (if any of the
x,y,z,p,t is set to e.g. a number it won't work anymore...):

Mathematica 4.1 for Linux
Copyright 1988-2000 Wolfram Research, Inc.
 -- Motif graphics initialized -- 

In[1]:= expr = Sin[x + y] + z/p - t;

In[2]:= Union[Cases[expr, _Symbol, Infinity]]

Out[2]= {p, t, x, y, z}

In[3]:= x=8;

In[4]:= Union[Cases[expr, _Symbol, Infinity]]

Out[4]= {p, t, y, z}

In[5]:= Quit[]

expr = Sin[x+y]+ z/p - t 

Union[Cases[expr, _Symbol, Infinity]]


Albert


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