如何在 \begin{split} 中左对齐方程式

Question

我在使用以下代码时遇到对齐问题。我想知道如何使第三个方程像第一个和第二个方程一样左对齐。

\begin{subequations}\begin{align}         
j_{11}&=\frac{\partial \dt u^H}{\partial u^H}=\theta^H(\alpha_1^\prime \pi^H+\alpha_2^\prime-1)\lessgtr 0\label{eq:jacobian_11}\\
j_{12}&=\frac{\partial \dt u^H}{\partial u^L}=\theta^H k (\alpha_1^{\prime\prime} \pi^L+\alpha_2^{\prime\prime})>0\\
\begin{split}
j_{13}=\frac{\partial \dt u^H}{\partial k}=\theta^H(\alpha_1^\prime\pi^H+\alpha_2^\prime-1)\frac{\partial u^H}{\partial k}\\
+\theta_H\bigg[\alpha_0^{\prime\prime}+\big(\alpha_2^{\prime\prime}\pi^L+\alpha_2^{\prime\prime}\big)u^L-\alpha_2^{\prime\prime}i^L+k(\alpha_1^{\prime\prime}\pi^L+\alpha_2^{\prime\prime}\big)\frac{\partial u^L}{\partial k}\bigg]\lessgtr 0\label{eq:jacobian_13}
\end{split}\end{align}\end{subequations}

请参考附件。

Answer 1

您还需要&在第 3 行和第 4 行添加明确的对齐点，而不仅仅是在第 1 行和第 2 行。

\documentclass{article} % or some other suitable document class
\usepackage{mathtools,amssymb}
\newcommand\dt{\,\mathrm{d}t} % ??
\begin{document}
\begin{subequations}
\begin{align}         
j_{11}&=\frac{\partial \dt u^H}{\partial u^H}=\theta^H(\alpha_1' \pi^H+\alpha_2'-1)\lessgtr 0\label{eq:jacobian_11}\\
j_{12}&=\frac{\partial \dt u^H}{\partial u^L}=\theta^H k (\alpha_1'' \pi^L+\alpha_2'')>0\\
\begin{split}
j_{13}&=\frac{\partial \dt u^H}{\partial k}=\theta^H(\alpha_1'\pi^H+\alpha_2'-1)\frac{\partial u^H}{\partial k}\\
&\quad+\theta_H\bigg[\alpha_0''+\bigl(\alpha_2''\pi^L+\alpha_2''\bigr)u^L-\alpha_2''i^L+k(\alpha_1''\pi^L+\alpha_2''\bigr)\frac{\partial u^L}{\partial k}\bigg]\lessgtr 0\label{eq:jacobian_13}
\end{split}
\end{align}
\end{subequations}
\end{document}