Math & Science ⇒ Question regarding mathematical typesetting

[drgz]

Hello,

just a quick question regarding mathematical typesetting. After reading this article on TUG, I have the impression that most sub/superscripts are supposed to be in upright/roman. I quote from the article:

Sub and superscripts that do not represent
physical quantities or mathematical variables
should be set in roman type; the amsmath package
makes available the command \text for setting
in roman type any word or sentence within
mathematics, also in sub and superscripts.

Now, the question is. Given that I, i.e., have a formula like (just writing LaTeX-code):

V_in = V_s\frac{Z_in}{Z_in+Z_s},

where the sub-script "s" denotes the source of the signal V_s; should all the sub-scripts in these formula be typeset in upright/roman? Or am I interpreting the article incorrectly?

I mean, the sub-script "in" does not represent a physical quantity IMO, and the sub-script "s" is neither a physical quantity or a mathematical variable? However, if I were to have a sub-script "k", denoting the index in for example some vector/matrix operation, then it should be typeset in italic, as it then would represent a mathematical variable, "k"?

I know some will say it's silly of me to bother with this, but I'd prefer to get it right, even though the readers of the text most likely won't care.

Help is greatly appreciated!

Best regards,

D.

[gmedina]

Hi,

...I have the impression that most sub/superscripts are supposed to be in upright/roman...

That depends on which field do you work at. As a mathematician working in algebra, most of my sub/superscripts denote variables, so most of them don't go in roman type.

The rule given in the article is clear: if the sub/superindices do not represent physical quantities or mathematical variables, then use roman type.

...should all the sub-scripts in these formula be typeset in upright/roman? Or am I interpreting the article incorrectly?

As I said before, if the subscripts are not physical quantities nor mathematical variables, write them in roman type.

Just a warning: the \text command inherits the font currently in use, so it might produce the wrong outcome. For example; if you are inside a standard theorem-like environment (which uses italic font) then \text will (wrongly) produce italic type: I would recommend to use \textup to obtain in such instances; take a look at the following example:

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\newtheorem{theo}{Theorem}

\begin{document}

%wrong outcome (subscript in italic type)
\begin{theo}
$V_{\text{in}}$
\end{theo}

%right outcome (subscript in roman type)
\begin{theo}
$V_{\textup{in}}$
\end{theo}

\end{document}

[drgz]

Thanks for the reply. Then I think that I've understood it correctly. The reason I doubted it was due to a disagreement with a fellow student, who interpreted the term "physical quantity" different than myself; so I wanted to check with a third party.

And also a big thanks for the heads up regarding \text and \textup. I hadn't noticed that at all.

Best regards,

D.