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  • upright Greek letters for constants as opposed to variables

    From Phillip Helbig (undress to reply)@21:1/5 to All on Sun Apr 26 15:05:47 2020
    Some journals require upright Greek letters for constants as opposed to variables, for example $\upi$ when used to denote 3.14159... as opposed
    to a variable ($\pi$ is sometimes used to denote parallax in astronomy,
    for instance). (Some journals define \upi as "upright pi", \upi as
    "upright i", and so on.)

    I certainly agree that LABELS should be upright (though they are usually
    Latin not Greek) and not italic to distinguish them from variables, e.g. $T_{mathrm{eff}}$ for effective temperature or $\rho_{textrm{g}}$ for
    gas density, say, as opposed to $G_{\mu\nu}$ where $\mu$ and $\nu$ are
    not constants but variables.

    And it is not just Greek letters. For example, e for the Euler number
    or i for the square root of -1 should also not be in math italic, to distinguish them from variables. I tend to agree with that as well.
    Also, units should be upright, e.g. 5 m and not $5m$ for 5 metres.

    On the other hand, I have never seen the gravitational constant $G$,
    which is even by definition a constant and not a variable, written
    upright. Ditto for the Hubble constant $H$ and so on.

    Or is there a difference between mathematical constants and physical
    constants?

    Perhaps because standard (La)TeX provides Greek letters only in math
    italic, upright Greek letters are less common than upright Latin
    letters, even when used in the same way (labels, units, symbols which
    are not variables).

    When writing for a specific journal, one usually has to follow the house
    style. However, if there is no rule, I prefer to do what is generally
    deemed to be correct. What is generally deemed to be correct here?

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  • From Hans Aberg@21:1/5 to All on Fri May 15 20:09:30 2020
    On 2020-04-27 00:05, Phillip Helbig (undress to reply) wrote:
    Some journals require upright Greek letters for constants as opposed to variables, for example $\upi$ when used to denote 3.14159... as opposed
    to a variable ($\pi$ is sometimes used to denote parallax in astronomy,
    for instance). (Some journals define \upi as "upright pi", \upi as
    "upright i", and so on.)
    ...
    Or is there a difference between mathematical constants and physical constants?

    The principle probably comes from pure mathematics, but even there, historically, they have not been available, just as well certain styles,
    such as bold italic, for the simple reason that it was expensive in led typesetting to keep them. Some journals would though have them, and one
    could mark up the manuscript to get the right one.

    Unicode changed that by adding those as characters (code points), in
    addition adding some styles that are not properly semantic, like sans
    serif and monospace variations. (The sans serif style is used for
    tensors by some engineers, but I have found no example in mathematics,
    physics or computer science of that.)

    [[Mod. note -- Checking a few general-relativity textbooks, I see that
    Misner, Thorne, & Wheeler "Gravitation" (W.H. Freeman, 1973) uses sans
    serif for tensors and differential forms, but none of the other books
    I checked do this.
    -- jt]]

    So when those are available, one can experiment with adhering to this principle, upright for constants and italic/slanted for variables.

    In some cases it may not be immediately clear what to use: Unicode
    unifies the upright style with the original language letters.

    TeX, by contrast, translates them automatically to italic in math mode.
    For Greek, it only has the slanted styles, and in addition not the
    uppercase letters that look like the Latin.

    Perhaps because standard (La)TeX provides Greek letters only in math
    italic, upright Greek letters are less common than upright Latin
    letters, even when used in the same way (labels, units, symbols which
    are not variables).

    So I switched typing these mathematical styles directly in the input
    file, and the fastest way to do that, both to implement and use, I found
    is to use text substitutions. Then the LaTeX unicode math package was insufficient, so I switched to ConTeXt.

    When writing for a specific journal, one usually has to follow the house style. However, if there is no rule, I prefer to do what is generally
    deemed to be correct. What is generally deemed to be correct here?

    You will have to experiment with it a bit.

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  • From Hans Aberg@21:1/5 to Mod on Sat May 23 11:10:00 2020
    On 2020-05-16 05:09, Mod wrote:
    Unicode changed that by adding those as characters (code points), in
    addition adding some styles that are not properly semantic, like sans
    serif and monospace variations. (The sans serif style is used for
    tensors by some engineers, but I have found no example in mathematics, physics or computer science of that.)

    [[Mod. note -- Checking a few general-relativity textbooks, I see that Misner, Thorne, & Wheeler "Gravitation" (W.H. Freeman, 1973) uses sans
    serif for tensors and differential forms, but none of the other books
    I checked do this.
    -- jt]]

    They use bold sans-serif when not having indices, but switches to
    non-bold serif, that is, plain italic, when having indices on the same
    object. In mathematics, like in differential geometry, one uses serifs
    and not switching styles, like between plain and bold, allowing the
    styles to be used for more different types of objects objects.

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