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Re: what would cause a symbol not to clear using Clear[name] or Remove[name]?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127228] Re: what would cause a symbol not to clear using Clear[name] or Remove[name]?
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Tue, 10 Jul 2012 00:41:10 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
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  • References: <jtd3al$9fq$1@smc.vnet.net>

On 08/07/2012 23:58, Nasser M. Abbasi wrote:
> Any experts here would explain why such a strange thing can happen?
>
> I do Clear[y] and then do ??y and it still shows the same expression as before.
>
> I also tried Remove[y], and it is still not clearing.
>
> --------------------------
> In[132]:= Clear[y]
>
> In[133]:= y
> Out[133]= 1/208694150 (0. -3.53899*10^6 x+63800. x^3+12500/3 (-7.5+x)^4 UnitStep[-7.5+x]-12500/3 (-0.9+x)^4 UnitStep[-0.9+x])
>
> In[134]:= Remove[y]
> In[135]:= y
> Out[135]= 1/208694150 (0. -3.53899*10^6 x+63800. x^3+12500/3 (-7.5+x)^4 UnitStep[-7.5+x]-12500/3 (-0.9+x)^4 UnitStep[-0.9+x])
>
> In[136]:= ??y
> Global`y
> y=(0. -3.53899*10^6 x+63800. x^3+12500/3 (-7.5+x)^4 UnitStep[-7.5+x]-12500/3 (-0.9+x)^4 UnitStep[-0.9+x])/208694150
>
> In[140]:= Clear["Global`*"]
> In[141]:= y
> Out[141]= beamDeflection[10,0.09,0.25,0.5,100000,0,29000000000,143927/20000000,1,x]
>
> In[142]:= Remove["Global`*"]
> In[143]:= y
> Out[143]= beamDeflection[10,0.09,0.25,0.5,100000,0,29000000000,143927/20000000,1,x]
> --------------------------------
>
> ?Remove
> removes symbols completely, so that their names are no longer recognized by Mathematica.
>
> In[139]:= $Version[]
> Out[139]= 8.0 for Microsoft Windows (64-bit) (October 6, 2011)[]
>
> Here is a video of it in this folder, but it is 70 MB AVI file (in need
> to figure out how to reduce the size of an AVI file). This in
> case someone thinks I am making this up :)
>
> http://12000.org/tmp/070812/
>
> Only after I close the kernel, will this symbol finally clear up.
>
> In[2]:= y
> Out[2]= y
>
> Do you think this is strange? or is there a rational explanation to it?
> I have thought always that Clear[] will clear a symbol.
>

Try executing

??Clear

??Remove

Just to see if you have somehow removed the protection on these symbols 
and redefined them.

Do you automatically load anything?

Does this happen immediately on startup:

y=42;

Clear[y]

y

Or only after you ran something?

David Bailey
http://www.dbaileyconsultancy.co.uk




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