Re: Re: How to clear OverBar[p]
- To: mathgroup at smc.vnet.net
- Subject: [mg30245] Re: [mg30199] Re: How to clear OverBar[p]
- From: BobHanlon at aol.com
- Date: Fri, 3 Aug 2001 00:56:14 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 2001/8/2 5:05:18 AM, mrMICE.fi at cbs.dk writes: >Sorry, I have just one more question. > >Normally I clear variables before assigning values so no mistakes are made. >But the > >Use Unset >Overbar[p] > >only works when Overbar[p] has assigned a value otherwise you will get >an >error/warning. Is there a way to avoid this, like asking if a variable >is >already assigned a value. > Since you are going to clear it anyway, you can assign it any arbitrary value prior to clearing it. In[1]:= SetAttributes[myUnset, HoldFirst]; myUnset[x_] := (x = 0; x=.); OverBar[p] does not have a value: In[3]:= OverBar[p] Out[3]= OverBar[p] myUnset does not result in a warning: In[4]:= myUnset[OverBar[p]] Assigning OverBar[p] a value In[5]:= OverBar[p] = 5 Out[5]= 5 Verifying the value: In[6]:= OverBar[p] Out[6]= 5 Clearing the value: In[7]:= myUnset[OverBar[p]] Verifying that it is cleared In[8]:= OverBar[p] Out[8]= OverBar[p] Bob Hanlon Chantilly, VA USA