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Re: clearing a variable with a dummy subscript

• To: mathgroup at smc.vnet.net
• Subject: [mg126576] Re: clearing a variable with a dummy subscript
• From: Peter Breitfeld <phbrf at t-online.de>
• Date: Sun, 20 May 2012 02:34:30 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <jp54mp$gos$1@smc.vnet.net>

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

• Follow-Ups:
  • Re: clearing a variable with a dummy subscript
    • From: Christoph Lhotka <christoph.lhotka@fundp.ac.be>