math expression inside math expression

Question

Let us assume the following example:

\documentclass{article}
\usepackage{amsmath}
\newcommand{\pt}{$p_{T}$}
\begin{document}

We analyse all cases of the transverse momentum \pt. First, let us 
assume that $p_{T} \leq 50 \text{GeV}$.

\end{document}

The result is

It is inviting to use the command \pt in the second mathematical expression and write it like that

$\pt \leq 50 \text{GeV}$

In case I do it, I get the error

! Missing $ inserted.
<inserted text> 
                $
l.6 ...omentum \pt. First, let us assume that $\pt
                                                   \leq 50 \text{GeV}$.

Suggestions?

And what exactly is the problem? Maybe you're using the wrong case of the command? (\pt is different of \pT) — Phelype Oleinik, Dec 25 '17 at 19:12

score 8 · Answer 1 · answered Dec 25 '17 at 19:16

The problem is that the \pt macro contains $...$ . The solution is to either use \ensuremath, so that the $...$ are added when needed,

\documentclass{article}
\usepackage{amsmath}
\newcommand{\pt}{\ensuremath{p_{T}}}
\begin{document}

We analyse all cases of the transverse momentum \pt. First, let us
assume that $p_{T} \leq 50 \text{GeV}$.

\end{document}

or to use:

\documentclass{article}
\usepackage{amsmath}
\newcommand{\pt}{p_{T}}
\begin{document}

We analyse all cases of the transverse momentum $\pt$. First, let us
assume that $p_{T} \leq 50 \text{GeV}$.

\end{document}

Personally, I prefer the latter because explicit is better than implicit and because this will probably work better with the syntax highlighter in your editor. See also When not to use \ensuremath for math macro?.

The second way is the correct one. Math should always be math. Rather, siunitx should be used rather than the disputable \text. — egreg, Dec 25 '17 at 20:56

score 4 · Answer 2 · answered Dec 25 '17 at 19:16

4

The error is because you are nesting two math environments. Change you command definition to:

\newcommand{\pt}{\ensuremath{p_{T}}}

answered Dec 25 '17 at 19:16

Phelype Oleinik

70,814

Answer from @Zarko contains an additional important information on \xspace therefore I change the "Accepted answer". – Viesturs Dec 30 '17 at 22:46

score 3 · Accepted Answer · answered Dec 25 '17 at 19:16

3

\documentclass{article}
\usepackage{amsmath}
\usepackage{xspace}
\newcommand{\pt}{\ensuremath{p_T^{}}\xspace}
\begin{document}

We analyse all cases of the transverse momentum \pt. First, let us
assume that $\pt \leq 50 \text{GeV}$.

\end{document}

xspace ensure correct spacing after use of \pt.

answered Dec 25 '17 at 19:16

Zarko

296,517

\xspace, I see, is indeed important. But the use of ^{} I don't understand. – Viesturs Dec 30 '17 at 22:04
@Viesturs, compare $p_T$ and $p_T^{}$, and observe difference. i prefer the second result :-) – Zarko Dec 30 '17 at 22:24
It seems that T is lower if ^{} is used. – Viesturs Dec 30 '17 at 22:30
1

@Viesturs, yes. ^{} push subscripts down and with this prepare more space for superscripts (which in this case is not used). similar effect you can obtain with use of package subdepth. – Zarko Dec 30 '17 at 22:43
I consider \xspace as important therefore I shift "Accepted answer" to this answer. – Viesturs Dec 30 '17 at 22:45

math expression inside math expression

3 Answers3