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Re: clearing a variable with a dummy subscript
Posted:
May 19, 2012 5:44 AM
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Am 18.05.2012 11:27, schrieb Andre Hautot:
> Hi !
> Here is something very simple I don't understand :
>
> f[x_] := x; f[2] (*A function*)
> 2
>
> Clear[f]; f[2] (*The same perfectly cleared as expected*)
> f[2]
>
>
> Subscript[u, k_] := k; Subscript[u, 2] (*u with subscript k_
> entered via the palette*)
> 2
>
> Clear[u]; Subscript[u, 2] (*I found no way to clear u; a
> suggestion ?)
> 2
>
Use:
Subscript[u, k_] =.
or (if you don't have other definitions for Subscript you want to keep):
Clear[Subscript]
the deeper reason is that this rule is stored in the DownValues of
Subscript:
Subscript[u, k_] := k;
DownValues[Subscript]
What you probably want to do is to store it as an UpValue to u instead
of a DownValue of Subscript:
u /: Subscript[u, k_] := k
DownValues[Subscript]
UpValues[u]
now you can get rid of the definition as expected:
Clear[u]
Subscript[u,2]
hth,
albert
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