Re: Character for e, 2.71828...

From: Kenneth Whistler (kenw@sybase.com)
Date: Mon Apr 08 2002 - 14:32:58 EDT


Elliotte Rusty Harold asked:

> > Does anybody happen to know the appropriate
> > Unicode character for the
> > base of the natural logarithms, e?

Various people answered:

U+0065.

Stefan responded:

> Actually, this should be an italic 'e'.

Here is a complete answer.

As John Jenkins pointed out:

> Except in rare cases for backwards
> compatibility with other
> standards, Unicode does not include special
> characters for mathematical or
> physical constants.

This is just as true for 'e', the base for natural
logarithms, as it is for 'c', the speed of light.
Note that in both cases, I have just used ASCII characters
in email for these constants, and if this mail gets converted
to Unicode on your Windows systems, those will be U+0065
and U+0063, respectively.

However, in mathematical and technical typesetting, such
constants are typically displayed italic, as Stefan pointed out.
Ordinarily, one could just apply the same styles as one would
use for <ital>markup</ital> in text and get acceptable results.

But in some specialized mathematical formula processing
applications, and basically only in such applications, Unicode
has also supplied the mathematical alphanumeric characters,
so that specialty mathematical applications don't need to
carry around all this stylistic information on a character-by-
character basis in formulae. For *those* applications only,
one could use:

U+1D450 MATHEMATICAL ITALIC SMALL C
U+1D452 MATHEMATICAL ITALIC SMALL E

Finally, in Unicode 3.2, because of another specialty application --
the use of double-struck italic forms for a few common mathematical
constants and the derivative, in patent applications and the like,
a few more letterlike characters have been added. Among them is:

U+2147 DOUBLE-STRUCK ITALIC SMALL E

*That* one you will find being used to express the base of the
natural logarithm in such documents. The constraints on its
use should be considered similar to those for use of the mathematical
italic series on Plane 1.

However, as Mark intimates in his Unicode myths list, the Unicode
Standard is not about standardizing *constants* of nature -- that
is the physicists' and other scientists' business. The Unicode
Standard is about standardizing *characters*, and there is no need
to have a separate character for every constant. In fact, there
is every reason *not* to have separate characters for them. I
don't want a "G" for the gravitational constant not to match
on a text search with the "G" in "Gravity" or "Google".

--Ken



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