[Tex/LaTex] Abbreviations in math mode

math-modespacingxspace

I am trying to adapt Martin Scharrer's solution from Macros for common abbreviations to be able to use them in math mode. Yes I realize I am about to incur some criticism that I should just use \text{}, but I'd prefer the macros to do the thinking for me.

I have three different versions of the \ie macro below and not sure which one is the correct one to use. The third one (\ieC, which is what I have been using) seems to yields slightly different spacing.
I am not able to figure out how to adapt the \etc macro for math mode to properly handle the case where there is a subsequent period as in \etc.. Furthermore, it appears as if the addition of \ifmmode screws up the \etc macro such that it no longer works properly even in text mode if there is a trailing period.

If there was a version of the \xspace macro that worked in math mode that would be great.

References:

Code:

\documentclass{article}

\usepackage{amsmath}
\usepackage{xspace}

\newcommand*{\ieA}{%
\ifmmode%
    \text{i.e.}\ %
\else%
    i.e.\@\xspace%
\fi%
}%

\newcommand*{\ieB}{%
\ifmmode%
    \text{i.e.~}%
\else%
    i.e.\@\xspace%
\fi%
}%

\newcommand*{\ieC}{%
\ifmmode%
    \text{i.e. }%
\else%
    i.e.\@\xspace%
\fi%
}%


\makeatletter
\newcommand*{\etc}{%
    \ifmmode%
        \@ifnextchar{.}{\text{etc}}{\text{etc.}}%
    \else%
        \@ifnextchar{.}%
            {etc}%
            {etc.\@\xspace}%
    \fi%
}%
\makeatother

\begin{document}\noindent
    $\ieA x < 2$ \quad \verb|\text{i.e.}\ |\par\noindent
    $\ieB x < 2$ \quad \verb|\text{i.e.~}|\par \noindent
    $\ieC x < 2$ \quad \verb|\text{i.e. }|\par\noindent
    
    \medskip\noindent
    $a \ne 0, b \ne 0, \etc$\par\noindent
    $a \ne 0, b \ne 0, \etc.$\par\noindent

    \medskip\noindent
    $a \ne 0, b \ne 0, \text{\etc}$ \quad \verb|\text{\etc}|\par\noindent
    $a \ne 0, b \ne 0, \text{\etc.}$\quad \verb|\text{\etc.}|\par\noindent

    \bigskip
    \noindent
    Outside of math mode \verb|\etc| no longer works at the end of sentence
    
    \noindent
    You should eat more fruit, \ieA apples, bananas, \etc. Next sentence.
    
    \noindent
    You should eat more fruit, \ieA, apples, bananas, \etc but also tomatoes.
\end{document}

The above MWE was for testing purposes, so I agree that the abbreviations there are not necessary to be within the math environment in those cases. But for my actual use case is in display mode where it is clearer to put that text as part of the formula as opposed to on the next line. For example:

enter image description here

Best Answer

Your third version \ieC produces larger spacing since you have . in text mode, i.e., the period ends a sentence. Usually one would probably write i.e.\ $x<2$, which corresponds to your first version \ieA. But it's up to you what you choose. Maybe in display math you'll prefer the larger spacing.

As for your second question, your \etc doesn't work because it lacks \expandafter. You test the next character with \@ifnextchar, but have a look at your code: When in math mode, you test the \else, and else you test the \fi! I know, this is the point where programming TeX can drive you crazy. What you have to do: use \expandafter to get rid of \else and \fi so that the \@ifnextchar can actually see the next character.

Just as a side note: you should put some space between a \ne 0, and b \ne 0. Moreover, your code really contains a lot of %s that could be omitted. Here's my solution for \etc:

\documentclass{article}

\usepackage{amsmath}
\usepackage{xspace}

\makeatletter
\newcommand*{\textetc}{%
        \@ifnextchar{.}
            {etc}
            {etc.\@\xspace}%
}
\newcommand*{\mathetc}{%
        \@ifnextchar{.}
            {\text{etc}}
            {\text{etc.}}%
}
\makeatother

\newcommand*{\etc}{%
    \ifmmode
        \expandafter\mathetc
    \else
        \expandafter\textetc
    \fi
}

\begin{document}\noindent
    $a \ne 0,\ b \ne 0,\ \etc$\par\noindent
    $a \ne 0,\ b \ne 0,\ \etc.$\par\noindent

    \medskip\noindent
    $a \ne 0,\ b \ne 0,\ \text{\etc}$ \quad \verb|\text{\etc}|\par\noindent
    $a \ne 0,\ b \ne 0,\ \text{\etc.}$ \quad \verb|\text{\etc.}|\par\noindent

    \bigskip
    \noindent
    Outside of math mode \verb|\etc| works now at the end of sentences!

    \noindent
    You should eat more fruit, i.e.\ apples, bananas, \etc. Next sentence.

    \noindent
    You should eat more fruit, i.e., apples, bananas, \etc but also tomatoes.

\end{document}

Related Solutions

[Tex/LaTex] When not to use \ensuremath for math macro

Two objections come to mind:

If you don't know you will be entering math mode, then you may write something "semantically" correct that breaks.

For example:

\documentclass{article}
\newcommand\mathmacro[1][A]{\ensuremath{{#1}_1}}
\begin{document}
 \mathmacro[$x^2$] % The dollar signs *leave* math mode
\end{document}

What's going on here is that \mathmacro[$x^2$] expands to

\ensuremath{{$x^2$}_1}

which expands to (effectively)

\ifmmode
 {$x^2$}_1
\else
 ${$x^2$}_1$
\fi

and you can see that if you write it outside of math mode, the second branch is taken, so the first dollar sign brings you into math mode and the one at the front of $x^2$ takes you out of it, with the reverse operation happening afterwards. This gives an error.

Of course, you aren't supposed to do that, since \mathmacro is actually a "math macro usable in text mode", so you should think of the thing between the brackets of its argument as being in math mode. Alas, this confuses both the author and the text editor's syntax highlighting, since it is a nonstandard assumption.

Edit: I would define this macro as:

\newcommand\mathmacro[1][A]{{#1}_1}

and use it as:

$x^2$ sub one: $\mathmacro[x^2]$.

This way, the parts that are math are clearly math.

In the unlikely event that you or some package sets \everymath, you will be very surprised when your apparently text-mode macros start to look different.

On the subject of semantics, though, the issue is clear: \ensuremath breaks the separation between math and text, which are two very different things. TeX even has the distinction built in: different fonts, different spacing rules, different parsing rules. You can probably construct a lot more counterexamples by exploiting these.

What I mean by this is that in the following situation:

\documentclass{article}
\newcommand\mathmacro[1][A]{\ensuremath{{#1}_1}}
\begin{document}
 A sub one: \mathmacro

 \bfseries A sub one: \mathmacro
\end{document}

you may be surprised that the bold text does not extend to the contents of the apparently text-mode \mathmacro.

What I'm saying is not so much that \ensuremath actually breaks anything as that it violates your expectations to the point that it makes things harder rather than easier.

[Tex/LaTex] When to use Roman and Italic Font in Math

This is going to be opinion-based, so I'll first suggest a strategy for typing your document.

\usepackage{amsmath}

\newcommand{\func}[1]{\operatorname{\mathit{#1}}}  % or \mathrm
\newcommand{\const}[1]{\mathit{#1}}                % or \mathrm
\newcommand{\wsub}[1]{\mathrm{#1}}                 % 'word' subscript

Then you can type

$\func{letter}(\sigma,c)\equiv\func{startmarker}(c)$
$\func{only}_{\wsub{free}}(\{c_{0}\})$

Of course you can add shorthands for the functions you use most often

\newcommand{\letter}{\func{letter}}
\newcommand{\startmarker}{\func{startmarker}}
\newcommand{\only}[1][]{%
  \func{only}%
  \if\relax\detokenize{#1}\relax _{\wsub{#1}}\fi
}

and the above formulas would be

$\letter(\sigma,c)\equiv\startmarker(c)$
$\only[free](\{c_{0}\})$

The definition of \only with an optional textual subscript can be simpler if xparse is used:

\usepackage{xparse}
\NewDocumentCommand{\only}{o}{%
  \func{only}%
  \IfValueT{#1}{_{\wsub{#1}}}%
}

Or you can opt for an even simpler \newcommand{\only}{\func{only}} and type

$\only_{\wsub{free}}(\{c_{0}\})$

Now my opinions. A function such as startmarker is not a “standard” function like max, log or sin. Those function names should always be typeset upright in order to emphasize their “fixed” meaning. The function you define in your document are not of universal use, so you can choose between upright or italic. Just be consistent and that's the purpose of the definitions I propose.

If you later decide that functions such as startmarker should be typeset upright, just remove \mathit from the definition of \func (or replace it by \mathrm, but since we are already under \operatorname this is not needed).

For constants it's a similar problem. I never typeset constants upright (that's something I leave to physicists), but I understand others can have different ideas.

Surely you won't place two multiletter constants next to each other without an explicit multiplication sign: so

\const{foo}\cdot\const{bar}

and not \const{foo}\const{bar}.