Re: DifferenitalD vs CapitalDifferenitalD

• To: mathgroup at smc.vnet.net
• Subject: [mg87938] Re: DifferenitalD vs CapitalDifferenitalD
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Mon, 21 Apr 2008 03:22:28 -0400 (EDT)
• Organization: The Open University, Milton Keynes, UK
• References: <fuees1\$bds\$1@smc.vnet.net>

```fizzy wrote:

> After applying Jens correction, I was hoping to be able to use the =
> DifferentialD  with x, etc. and then use the 'dx' , where 'd' here is =
> DifferentialD (just dont know how to add it here in the email),  so it =
> would be a Symbol....but this didnt work....I realize I can use the =
> straight forward   dx , etc.  symbol but I want to highlight the =
> Differential....any way to 'fix' this?....when I type in  DifferentialD =
> , from the Palette, and then add x to it and perform  //Head on it , it =
> just returns DifferentialD

<snip>

Hi Jerry,

The behavior you have noticed is perfectly normal since the built-in
function *DifferentialD[]*, which can also be entered as |esc|dd|esc|
(i.e. the escape key followed by the character lowercase d twice
followed by the escape key again), is a *compound operator with built-in
meaning*. The full form of a complete expression with *DifferentialD[]*
is DifferentialD[some_expression] (one argument is required).

For instance, say we enter the expression

|esc|dd|esc|z

Its full form is

FullForm[|esc|dd|esc|z] === DifferentialD[z]

Thus, one cannot manipulate double struck lowercase d independently.

Now, if you are interested by the above character without built-in
meaning, you can get it with the following sequence of keys:

|esc|dsd|dsd|

Note that dsd stands for double struck lowercase d. Similarly, you can
get a double struck capital C by entering |esc|dsC|esc|

Finally, enter and evaluate the following sequences of keystrokes:

|esc|int|esc|z |esc|dsd|esc|z

|esc|int|esc|z |esc|dd|esc|z

They look the same. However, the first expression generates an error
message, while the second returns the expected definite integral.

Regards,
-- Jean-Marc

```

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