Shortcut to writing out long, common, expressions?

Question

I'm writing an astronomy paper and have some symbols and variables which are common throughout. It's becoming cumbersome to write them out each time. Is there a way to create a shortcut of sorts for these? Note, most are in math-mode.

For example:
log(Hi)

$\log(\textrm{H}\textsc{i})$

log(SFR/M*)

$\log(\textrm{SFR} / \textrm{M}_{\odot})$

Answer 1

I would split the problem into two parts. First you define the elementary symbols, then expressions in terms of them:

\documentclass{article}
\usepackage{amsmath}

%% first the symbols
\newcommand{\Hi}{\textnormal{H\kern-.1em\textsc{i}}}
\newcommand{\SFR}{\mathrm{SFR}}
\newcommand{\Mo}{\mathrm{M}_{\odot}}
%% then common expressions
\newcommand{\lHi}{\log\Hi}
\newcommand{\lsfrmo}{\log(\SFR/\Mo)}

\begin{document}
\begin{gather*}
\log\Hi + \log(\SFR/\Mo)\\
\lHi+\lsfrmo
\end{gather*}
\end{document}

I've added some bit to the definition of \Hi just to show how you can redefine the elementary symbol without any need to modify also the definition of the expression defined in terms of it.

With \textnormal{...} we ensure the font will be the “initial” one, independently of the context. This is needed for \Hi, but not for \SFR; since \mathrm is more efficient than \textnormal, it's preferable when it's possible to use it.

Answer 2

Creating macros that provide shortcuts for frequently used strings is a very good idea. For an entry-level introduction to the uses of the LaTeX \newcommand directive see, e.g., Chapter 6, "Customizing LaTeX", of the guide The Not So Short Introduction to LATEX2e.

For instance, you could issue the instructions

\newcommand\loghi{\log(\mathrm{H}\textsc{i})}
\newcommand\sfrm{\log(\mathrm{SFR} / \mathrm{M}_{\odot})}

in the preamble and, later on in the body of the text, write something like

bleet bleet $\loghi=\sfrm$ more bleet bleet

As you've already noted in a comment, a complication arises if these macros can also be used in bold surroundings such as sectioning headers. Specifically, given the above definition of \loghi, LaTeX will try to typeset the letter i in bold-smallcaps. As you've discovered, if the font family you're using does not feature a bold-smallcaps font, the letter will be set in "ordinary" bold, i.e., as i. Not the desired effect, right?!

What to do? I think you have (at least) two options. The first is to use a font family that does feature a bold-smallcap font. Two such families arenewt xtext/newtxmath and newpxtext/newpxmath . The former provides a "Times Roman" look, the latter a "Palatino" look. This may (or may not...) be acceptable to you.

Second, you could set up the macro that defines \loghi in such a way that it won't even try to use a (possibly nonexistent) bold smallcaps glyph. For instance,

\newcommand\loghi{\log(\mathrm{H}\textsc{\mdseries i})}

(note the addition of \mdseries to the argument of \textsc) instructs LaTeX to apply \textsc to a "medium weight" (rather than a "bold weight") version of i. As long as the medium-weight font features smallcaps glyphs, you'll be guaranteed success.