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How to clear a variable with subscript?

Zhenyu Zeng

Posted 1 year ago

Hello, The subscript symbol can be assigned but can't be cleared. Subscript[a, 0] = 2 Clear[Subscript[a, 0]] cause error.

POSTED BY: Zhenyu Zeng

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Christopher Young

Christopher Young, CYInsight

Posted 1 year ago

Isn’t this where Remove is supposed to be used? That seems to get rid of a subscripted variable that’s been made into a symbol via the palette from the Notations package. https://stackoverflow.com/questions/8512120/difference-between-clear-and-remove-in-mathematica#:~:text=Remove%5Bsymbol1%2C%20...,string%20input%20that%20ClearAll%20supports.

POSTED BY: Christopher Young

Updating Name

Posted 1 year ago

Thanks for your advice. The `Remove` doesn't work for `Subscript`. Subscript[a, 0] = 7; Remove[Subscript[a, 0]] (Remove::ssym: Subscript[a, 0] is not a symbol or a valid string pattern.)

POSTED BY: Updating Name

Eric Rimbey

Posted 1 year ago

That's now how you'd use Remove. Remove can't remove an expression. It can only remove a symbol.

POSTED BY: Eric Rimbey

Zhenyu Zeng

Posted 1 year ago

Thanks.

POSTED BY: Zhenyu Zeng

Zhenyu Zeng

Posted 1 year ago

What is the difference between a normal expression and a symbol? Regards.

POSTED BY: Zhenyu Zeng

Rohit Namjoshi

Posted 1 year ago

In the WL everything is an expression. An expression is either an `Atom` or a normal expression. A normal expression is of the form h[e1, e2, ...] where `h` is the `Head`. `h`, `e1`, `e2`, ... are expressions - atoms or normal expressions. I don't think there are any exceptions to this structure.

POSTED BY: Rohit Namjoshi

Zhenyu Zeng

Posted 1 year ago

Thanks. So a symbol is a atom?

POSTED BY: Zhenyu Zeng

Michael Rogers

Michael Rogers, Emory University

Posted 1 year ago

POSTED BY: Michael Rogers

Updating Name

Posted 1 year ago

Thanks. Learned a lot.

POSTED BY: Updating Name

Eric Rimbey

Posted 1 year ago

POSTED BY: Eric Rimbey

Zhenyu Zeng

Posted 1 year ago

Okay. So, `Subscript[a,0]` definite `Subscript`. Subscript[a, 0] = 2 Information[Subscript] Superscript*5 Why isn't the last result of the codes 10 but `5 Superscript`?

POSTED BY: Zhenyu Zeng

Eric Rimbey

Posted 1 year ago

POSTED BY: Eric Rimbey

Zhenyu Zeng

Posted 1 year ago

Thanks. I am still a little confused. When there is a value in `DownValues`, multiplication should work normally.

POSTED BY: Zhenyu Zeng

Eric Rimbey

Posted 1 year ago

Multiplication is working normally (as in, the way Mathematica intends for it to work). Try 5 List (* 5 List ) `List` is a built in function, and it definitely has defined behavior when applied to arguments (aka DownValues), but when encountered in isolation, it's just a symbol. In the expression `Subscript5`, `Subscript` appears as an isolated symbol--it's not the head of any expression. So, Mathematica looks at `OwnValues`, finds nothing, and leaves `Subscript` alone. Try `5 Table` or `5 Integrate` or any other symbol that has no `OwnValues`. The multiplication cannot be resolved further so you just end up with `5 symbol`. When Mathematica encounters an isolated symbol, it consults `OwnValues` not `DownValues` to figure out what to do. Mathematica looks for `DownValues` when the symbol is the head of an expression.