I would like to have an equation for an equivalence where the left-hand side is centered and the right-hand side is spaced over multiple lines. Researching this so far only lead me to the answer on how to split up a regular equation in general.
How can I split an equation over two (or more) lines
what I am looking for is something like this
or with curly brackets that span two lines like so
How could I do this? Thank you
For the first problem, I suggest you employ an alignedat environment; for the second, I suggest you employ a cases environment. Both environments are provided by the amsmath package.
\documentclass{article}
\usepackage{mathtools} % for '\coloneqq' macro and access to the 'amsmath' package
\begin{document}
\[
x\in G \quad \iff \quad
\begin{alignedat}{2}
&g_i(x)\le0 \quad &&\text{ for } i\in I \coloneqq \{1,\dots,m\},\\
&h_j(x)=0 \quad &&\text{ for } j\in J \coloneqq \{1,\dots,p\}.
\end{alignedat}
\]
[
\mathbf{1}_A(x) \coloneqq
\begin{cases}
1 & \text{if $x\in A$,} \
0 & \text{if $x\notin A$.}
\end{cases}
]
\end{document}
