Consider the following MWE
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{gather*}
\renewcommand{\arraystretch}{1.2}
\begin{pmatrix} \frac{1}{2} \\ \frac{1}{2} \end{pmatrix} \\
\begin{pmatrix} \frac{1}{2} \\ \frac{1}{2} \end{pmatrix}
\end{gather*}
\begin{gather*}
\renewcommand{\arraystretch}{1.2}
\begin{pmatrix} \frac{1}{2} \\ \frac{1}{2} \end{pmatrix} \\
\renewcommand{\arraystretch}{1.2}
\begin{pmatrix} \frac{1}{2} \\ \frac{1}{2} \end{pmatrix}
\end{gather*}
\end{document}
The first gather
produces two arrays; in the first, the fractions are properly spaced, while in the second, they are crowded together with the default vertical spacing. Why do I need to re-specify \renewcommand{\arraystretch}{1.2}
after the newline? Is there a better way to do this? (I realize I could enclose the whole gather inside a {}
pair with a \renewcommand{\arraystretch}{1.2}
after the opening {
).
Best Answer
Each entry between line breaks inside the
gather
environment are placed inside a group. To that end, the scope of\renewcommand{\arraystretch}{1.2}
only lasts until the end\\
, after which you have to issue it again.A very similar problem is showcased when you use, for example
The bold switch (
\bfseries
) doesn't span further than\\
, and would have to be re-issued to have an effect.For the stretch to have a global effect across line breaks, you have to issue it outside the environment.