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Topic: clearing a variable with a dummy subscript
Replies: 5   Last Post: May 21, 2012 5:59 AM

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Peter Breitfeld

Posts: 424
Registered: 12/7/04
Re: clearing a variable with a dummy subscript
Posted: May 20, 2012 2:34 AM
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Andre Hautot wrote:

> 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
>
> Thanks in advance,
>
> ahautot
>
>


The values of supcripted Variables are not associated with u, but to
Subscript:

Subscript[u,2]=123

DownValues[u] returns: {}

DownValues[Subscript] returns: {HoldPattern[u_2]:>123}

So to Clear, you must call:

Clear[Subscript]

(but then *all* subscripted variables are cleared)

--
_________________________________________________________________
Peter Breitfeld | Bad Saulgau, Germany | http://www.pBreitfeld.de




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