On 5/18/12 at 5:25 AM, email@example.com (Andre Hautot) wrote:
>Hi ! Here is something very simple I don't understand :
>f[x_] := x; f (*A function*) >2
>Clear[f]; f (*The same perfectly cleared as expected*) f >
>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
Simply put, Subscript[u,2] is not a symbol (does not have head Symbol) in Mathematica. Consequently, things designed to work with symbols often don't work well with Subscript[u,2].
If you want to use Subscript[u,2] or something similar as a variable your best choice is to load the Notation package. Use the documentation center to locate the usage guide by searching on notation package.