Re: Subscript Variable

• To: mathgroup at smc.vnet.net
• Subject: [mg20315] Re: [mg20188] Subscript Variable
• From: "David Park" <djmp at earthlink.net>
• Date: Fri, 15 Oct 1999 20:20:44 -0400
• Sender: owner-wri-mathgroup at wolfram.com

```Michel,

A couple of months ago Carl Woll posted one solution to this problem. Essentially he
changed the Attributes of Subscript to HoldFirst, and added SubscriptInformation and
ClearSubscripts routines. I liked his routine so much I made a little package of it
and extended it slightly. Here are examples of it's use.

< Algebra`WollSubscripts`

?Algebra`WollSubscripts
"WollSubscripts sets the attributes of Subscript to HoldFirst so that it can \
be used like a symbol. Subscript definitions can be defined. The additional \
routines ClearSubscripts and SubscriptInformation are also provided."

?ClearSubscripts
"ClearSubscripts[sym1, sym2,...] will clear all Subscript definitions based \
on the symbols."

?SubscriptInformation
"SubscriptInformation[sym1, sym2,...] will print the Subscript definitions \
based on the symbols."

Here I use InputFormat so it will be readable in email.

Subscript[f, 1][x_] = x^2 + 1;
Subscript[f, 2][x_] = x^3 - 1;

SubscriptInformation[f]
Subscript[f, 1][x_] = 1 + x^2
Subscript[f, 2][x_] = -1 + x^3

?? Subscript
"Subscript has been given the Attribute HoldFirst so that it can be \
used like a symbol and be given definitions."
Attributes["Subscript"] = {HoldFirst}
Subscript[f, 1][x_] = 1 + x^2
Subscript[f, 2][x_] = -1 + x^3

Subscript[f, 2][y] - Subscript[f, 1][y]
-2 - y^2 + y^3

ClearSubscripts[f]
SubscriptInformation[f]
(none)

?? Subscript
"Subscript has been given the Attribute HoldFirst so that it can be \
used like a symbol and be given definitions."
Attributes["Subscript"] = {HoldFirst}

I am pasting the notebook that creates the package at the end of the email. The
package should be placed in the AddOns/ExtraPackages/Algebra directory.

David Park

>Hello,
>
>I have a problem about subscript variables.
>
>First Question :
>
>If I use a variable named Subscript[x,1] ,
>(typed in with Ctrl _)
>
>I can affect a value to this variable, get value of expressions
>involving this variable, clear this variable with . but not with Clear[]
>!
>
>This variable is not given when I ask Names["x*"] and I cannot get
>information on it with ?.
>
>
>Second Question :
>
>If I use such a variable in order to define a function with
>  f1[x_]=x^2+1
>I cannot clear the variable with f1=.
>(of course, just above f1 means Subscript[f,1])
>
>
>Thanks a lot for any help
>
>
>J.Michel CORNIL
>

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```

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