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

*To*: mathgroup at smc.vnet.net*Subject*: [mg127219] Re: what would cause a symbol not to clear using Clear[name] or Remove[name]?*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Sun, 8 Jul 2012 22:46:44 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

Here is an example of one way that can occur. y starts off clear ??y Global`y $Post is set to define y after any evaluation ($Post=(y=10;#)&); Now, even clearing y will set it Clear[y] ??y Global`y y=10 To stop this, $Post must be cleared (or close the kernel) $Post=. Clear[y] ??y Global`y Bob Hanlon On Sun, Jul 8, 2012 at 7:05 PM, Nasser M. Abbasi <nma at 12000.org> 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. > > thanks, > --Nasser