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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: [mg31135] Re: [mg31117] What variables are in a function and displaying surds
  • From: Tomas Garza <tgarza01 at prodigy.net.mx>
  • Date: Fri, 12 Oct 2001 03:36:55 -0400 (EDT)
  • References: <200110102314.TAA25717@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

One possibility for your first question (variables are listed in the order
in which they appear in the FullForm of the expression) :

In[1]:=
whichVariables[v_]:=
  Module[{a=List@@v, f},
     f[u_]:=Flatten[DeleteCases[List@@#,x_?NumericQ]&/@u];
    FixedPoint[f,a]]

In[2]:=
expr=Sin[x+y]+z/p-t;
In[3]:=
whichVariables[expr]
Out[3]=
{t,p,z,x,y}

In[4]:=
expr = Sin[x + Exp[y]]/Sqrt[z^(1/3)] - Cos[Sin[Tan[p]]];
In[5]:=
whichVariables[expr]
Out[5]=
{p,z,y,x}

In[6]:=
expr=Sin[c[x,y]];
In[7]:=
whichVariables[expr]
Out[7]=
{x,y}

Tomas Garza
Mexico City

----- Original Message -----
From: "Wonko the Sane" <michael_r_went at yahoo.com>
To: mathgroup at smc.vnet.net
Subject: [mg31135] [mg31117] What variables are in a function and displaying surds


> 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.
>
> Another unrelated question is when I use Mathematica V4.0 to calculate
> tables of ThreeJSymbols the outputs Generally consist of fractions of
> roots of the form
>
> Sqrt[a/b] , c/Sqrt[d] and Sometimes Sqrt[e/f]/g
>
> is there a way to force Mathematica always output them in the form
> Sqrt[h]/i
>
> eg instead of it giving Sqrt[2/3] giving Sqrt[6]/3
>
> Regards, Michael
>



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