[Tex/LaTex] How to left align sub-equations in which some sub-equations are split across multiple lines (with their own alignment)

alignline-breakingmath-mode

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.

Best Answer

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.

enter image description here

I have removed all \left and \right that serve no purpose here (they actually introduce unwanted spaces).

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