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Re: Disappearing variables

• To: mathgroup at smc.vnet.net
• Subject: [mg13800] Re: [mg13759] Disappearing variables
• From: "Jurgen Tischer" <jtischer at col2.telecom.com.co>
• Date: Fri, 28 Aug 1998 04:18:23 -0400
• Sender: owner-wri-mathgroup at wolfram.com

Hi Vilis,
I don't want to give the impression of the wise guy, I just fooled
around a bit. So:
1. Help on Remove says:
"If you have an expression that contains a symbol which you remove, the
removed symbol will be printed as Removed["name"], where its name is
given in a string. "
2. If you look at f after you removed x, it shows

In[1]:= ?f

"Global`f"
f := Removed["x"] = 123

So that's it, the definition of f is an expression. If your question is
not purely academic, maybe you could use Clear instead of Remove?

Jurgen

-----Original Message-----
From: nobody at News.Dal.Ca <nobody at News.Dal.Ca> To: mathgroup at smc.vnet.net
Subject: [mg13800] [mg13759] Disappearing variables


>I want to to define a variable inside a function, as follows: f:=x=123;
>Whenever I run f, x should be given the value of 123, and if x doesn't
>exist, it should be created. However:
>
>In[1]:= f:=x=123;
>In[2]:=f
>Out[2]:=123
>In[3]:=x
>Out[3]:=123        ** x exists
>In[4]:=Remove[x];
>In[5]:=f
>Out[5]:=123  ** f seems to work
>In[6]:=x
>Out[6]:=x     ** x doesn't exist anymore, even though f worked
>
>It seems like x is created when I initially define f, whereas since f is
>SetDelayed,  x should be created when I run f.  Does anyone know why x
>is not created when I run f?
>
>Vilis Nams
>
>
>