# How to left align sub-equations in which some sub-equations are split across multiple lines (with their own alignment)

I have a set of four sub-equations, which I each want numbered and left-aligned. The second and third of these sub-equations are too long for one line so I am using the split environment to manually add line breaks with appropriate alignment where appropriate. I can't figure out how to do this.

Here's what I have now:

\begin{subequations}
\label{eq:omegai}
%
\begin{gather}
\label{eq:omega0}
\Omega_0 = \left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} > \omega_t \right\}
\\
%
\label{eq:omega1}
\begin{split}
\Omega_1 = &\left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} > \omega_t \right\} \\
&\cup \left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} > \omega_t \right\} \\
&\cup \left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} \leq \omega_t \right\}
\end{split}
\\
%
\label{eq:omega2}
\begin{split}
\Omega_2 = &\left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} \leq \omega_t \right\} \\
&\cup \left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} \leq \omega_t \right\} \\
&\cup \left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} > \omega_t \right\}
\end{split}
\\
%
\label{eq:omega3}
\Omega_3 = \left\{\left(\omega_{12},\omega_{23}\right) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} \leq \omega_t \right\}
\end{gather}
%
\end{subequations}


I have tried changing gather to align, but I get only the first and fourth equation left-aligned and the others are smashed to the right.

• It would be helpful if you edited your code and provided a fully compilable MWE including \documentclass and the appropriate packages that sets up the problem. While solving problems can be fun, setting them up is not. Then, those trying to help can simply cut and paste your MWE and get started on solving the problem. – Peter Grill Apr 14 '15 at 22:01

Use align, not gather:

\documentclass{article}
\usepackage{amsmath}
\newcommand{\suchthat}{\mid}

\begin{document}
\begin{subequations}
\label{eq:omegai}
%
\begin{align}
\label{eq:omega0}
\Omega_0 ={}& \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} > \omega_t \}
\\
%
\label{eq:omega1}
\begin{split}
\Omega_1 ={}& \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} > \omega_t \} \\
& \cup \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} > \omega_t \} \\
&\cup \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} \leq \omega_t \}
\end{split}
\\
%
\label{eq:omega2}
\begin{split}
\Omega_2 ={}& \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} > \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} \leq \omega_t \} \\
& \cup \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} > \omega_t,\ \hat{\omega}_{31} \leq \omega_t \} \\
& \cup \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} > \omega_t \}
\end{split}
\\
%
\label{eq:omega3}
\Omega_3 ={}& \{(\omega_{12},\omega_{23}) \suchthat \hat{\omega}_{12} \leq \omega_t,\ \hat{\omega}_{23} \leq \omega_t,\ \hat{\omega}_{31} \leq \omega_t \}
\end{align}
%
\end{subequations}
\end{document}


The ={}& trick is to get \cup a bit to the right of the brace in the upper line in the split equations. I have removed all \left and \right that serve no purpose here (they actually introduce unwanted spaces).