1

How do writers typeset their equations of the form (EQUATION), (WORDS)(EQUATION), where the latter part usually serves as a condition or explanations?

For example, example

Is the only way of doing this to write something like $$\begin{...}\;\;\;\text{ for some }\gamma...$$?

justadzr
  • 113

2 Answers2

5

The idea is that, yes. However it's better to use a predefined spacing command rather than arbitrary rows of \; commands (that are for different things).

You can improve your style by using some personal command: I defined \Mat for a set of matrices (with an upright M) and \ZZ for the integers.

The reason for the indirect definition is that if you have several number sets to deal with, just changing the main command \numberset to use, say, \mathbf, you'll get all number sets updated and don't need to change each one of them.

enter image description here

\documentclass{article}
\usepackage{amsmath,amssymb}

\DeclareMathOperator{\Mat}{M}
\newcommand{\numberset}[1]{\mathbb{#1}}
\newcommand{\ZZ}{\numberset{Z}}


\begin{document}


\begin{equation}
\begin{bmatrix} P \ Q \end{bmatrix}
= \gamma \begin{bmatrix} \omega_1/N + \Lambda \ \omega_2/N + \Lambda \end{bmatrix}
\quad\text{for some $\gamma \in \Mat_2(\ZZ/N\ZZ)$}
\end{equation}


\end{document}

Don't use \text{M}: it is wrong in this context; for example, the M would be in italic in the statement of a theorem. Also \tag is for a very different purpose and should not be abused.

egreg
  • 1,121,712
3

If you meant for the equation to be in display mode, you can use \tag*. For example:

\documentclass[preview]{standalone}
\usepackage{amssymb}
\usepackage{amsmath}

\begin{document}
This is an equation:
[
\begin{bmatrix}
    P\ 
    Q
\end{bmatrix}
= \gamma
\begin{bmatrix}
    \omega_1/N + \Lambda \
    \omega_2/N + \Lambda 
\end{bmatrix}
\tag*{for some $\gamma \in \text{M}_2(\mathbb{Z}/N \mathbb{Z})$}
]
\end{document}

The above code yields:

Minimal working example

Note that \tag* does not include parentheses. To include surrounding parentheses in the tagged remark, remove the asterisk from the command (i.e., use \tag).

As an aside, avoid using $$...$$ in display math mode, as it is heavily discouraged. See here and here for very good explanations why.

John
  • 307
  • 1
  • 7