Re: Variables?
- To: mathgroup at yoda.physics.unc.edu
- Subject: Re: Variables?
- From: jfh124 at rsphy1.anu.edu.au (jason harris)
- Date: Sun, 30 May 1993 20:24:29 -0500
Levent Kitis writes...
>Is the following a bug or is Variables[..] supposed to work this way?
>In[1]:= p[x_] := 1 + E x + Pi x^2
>In[2]:= Variables[p[x]]
>Out[2]= {E, Pi, x}
No this is not a bug. In expression In[2], p[x] evaluates to 1 + E x + Pi
x^2. Then it returns Variables[1 + E x + Pi x^2], which is {E, Pi, x}. If
you wamted to know the variable inside the head you could define
In[1]:=
MyVariables[h_[x__]]:={x};
SetAttributes[MyVariables,HoldAll]
(* this attribute HoldAll makes sure that h[x] is not evaluated and *)
(* will match the pattern *)
then,
In[2]:= MyVariables[p[x,y]]
Out[2]= {x,y}
In[3]:= MyVariables[p[x]]
Out[3]= {x}
hope this helps,
Jason
$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%
Jason Harris jfh124 at rsphysse.anu.edu.au
Optical Sciences Center
Australian National University
ACT 0200, Canberra Tel.: 495-0191
Australia. Fax.: 249-5184
$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?$ at %?$@%?