equationsitalicmath-mode
I am writing an equation, and I want some of the characters to not be italicized. All the other questions similar to this seem to be about globally changing italicizing in equations, but I just have 2 letters I don't want to be italic. The equation isn't in line, so I can't just end the equation and start a new one.
For example, say I'm writing $$f(x) = x^2$$, but I want the f, and only the f, to be non-italicized. How can I do this?
On a case-by-case basis, it is possible to typeset text within math mode using \textrm{...} or \mathrm{...}, the latter being used predominantly for typesetting units or symbols and not pure text (since it gobbles spaces that are not escaped). \mbox{...} is another alternative to \textrm{...}, since it resets its contents to text mode by default. Here are some examples:
\documentclass{article}
\begin{document}
Here is a formula: $x=\exp(\log \mathrm{x})$
Here is another: $\sin^2 t+\cos^2 t = \textrm{famous identity}$
\end{document}
The above font changes do not work that well in general, since switching to a different font when using sub- and superscripts, say, does not always scale as expected. There are ways around it though. For example, using \text{...} from the amstext package (automatically loaded by amsmath - see the AMS package dependencies), which switches to the appropriate font size via \mathchoice:
\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
% amsmath loads the amstext package by default
\begin{document}
Here is a formula: $x=y^{abc}$
Here it is again: $x=y^{\mbox{abc}}$
Compare that to: $x=y^{\text{abc}}$
\end{document}
This is my suggestion:
\documentclass{article}
\usepackage{amsmath}
\usepackage{siunitx}
\begin{document}
\begin{equation*}
P_{\text{AVG}} = \SI{19.5}{\micro\watt} + \frac{\SI{2180}{\micro\joule}}{5 \cdot \SI{60}{\second} + \SI{0.2}{\second}} = \SI{26.77}{\micro\watt}
\end{equation*}
\end{document}
(By loading the amsmath package, I can use text to typeset the "AVG" subscript in roman)
Best Answer
As mentioned in the comments,
\mathrm{f}will insert a letter from the text font as a math symbol. Here’s an example set in ISO style in legacy NFSS mode. The constants i, e and π are all upright, but the variable x is italic. You’ll notice that the upright letters are the same as from the text font. It would be possible to select another font as\mathrm, for example withisomath.The
unicode-mathpackage distinguishes between text letters in math mode (\mathrm) and upright math symbols (\symup). However, you need to change the upright math alphabet to notice any difference in appearance. Here is an example that replaces the upright math symbols with CMU Serif Upright Italic, an unslanted version of the Computer Modern italic font. (Except for the digits, because$10$and10should stay the same.) Notice thatunicode-mathis able to tell the difference between upright math symbols and operator names.I think the result matches pretty well, but Knuth’s Computer Modern italic font was never intended to be unslanted. (The tail of the e did not originally stick out like that.) So here’s another example, which combines Asana Math with upright math letters from Neo Euler. These are clones of two famous fonts by Hermann Zapf (Palatino and AMS Euler) that complement each other very nicely. The text font (also used for operator names) is another clone of Palatino.