如何在子方程式前添加文本？

Question

我正在将一本书翻译成中文，但翻译公司没有提供这本书的 latex 文件。如何在子方程式前添加文本？

这是我的代码

\parbox{8.5em}{
    predictor: \\
    Kalman gain: \\
    corrector: 
} 
\parbox{8.5em}{
\begin{subequations}
\begin{align}
    \check{\mathbf{P}}_k &= ...\\
    \check{\mathbf{x}}_k &= ...\\
    \mathbf{K}_k  &= ...\\
    \hat{\mathbf{P}}_k  &= ...\\
    \hat{\mathbf{x}}_k  &= ...
\end{align}
\end{subequations}
}

它和书中展示的版本不一样。

Answer 1

使用以下快速解决方案eqnarray（不太推荐）：

\documentclass{article}
\usepackage{amsmath,multirow}
\begin{document}

\begin{subequations}
\begin{eqnarray}
 \multirow{2}{*}{predictor:}  &\Check{\mathbf{P}}_k = ...\\
                              &\Check{\mathbf{x}}_k = ...\\
 \text{Kalman gain:}          &\mathbf{K}_k       = ...\\
 \multirow{2}{*}{corrector:}  &\hat{\mathbf{P}}_k = ...\\
                              &\hat{\mathbf{x}}_k = ...
\end{eqnarray} 
\end{subequations}

\end{document}

更好的选择是使用align：

\begin{subequations}
\newcommand{\hleft}{\hspace{-6em}}
\begin{align}
 \multirow{2}{*}{predictor:} &\hleft& \Check{\mathbf{P}}_k &= ...\\
                             &\hleft& \Check{\mathbf{x}}_k &= ...\\
 \text{Kalman gain:}         &\hleft& \mathbf{K}_k         &= ...\\
 \multirow{2}{*}{corrector:} &\hleft& \hat{\mathbf{P}}_k   &= ...\\
                             &\hleft& \hat{\mathbf{x}}_k   &= ...
\end{align} 
\end{subequations}

Answer 2

两种解决方案，包括\alignat和mathtools，以及一些手动调整：

\documentclass{article}
\usepackage{array}
\usepackage{mathtools}

\begin{document}

\begin{subequations}
  \begin{alignat}{2}
                                                                       & & \check{\mathbf{P}}_k & = ... \\[-1.2ex]
    \ArrowBetweenLines[\llap{\raisebox{-0.8ex}[0pt][0pt]{predictor:}}] & \qquad & \check{\mathbf{x}}_k & = ... \\[0.5ex]
    \llap{Kalman gain:\quad} & & \mathbf{K}_k & = ... \\
                                                                       & & \hat{\mathbf{P}}_k & = ... \\[-1.2ex]
    \ArrowBetweenLines[\llap{\raisebox{-0.8ex}{corrector:}}] & & \hat{\mathbf{x}}_k & = ...
  \end{alignat}
\end{subequations}

\begin{subequations}
  \begin{alignat}{2}
                                                                                                 & & \check{\mathbf{P}}_k & = ... \\
                                                                                                 & & \check{\mathbf{x}}_k & = ... \\
    \llap{\raisebox{1.2ex}[0pt][0pt]{\setlength{\extrarowheight}{3ex}\begin{tabular}{r}predictor: \\[-0.5ex]Kalman gain: \\corrector:
        \end{tabular}}} & \qquad & \mathbf{K}_k & = ... \\
                                                                                                 & & \hat{\mathbf{P}}_k & = ... \\
                                                                                                 & & \hat{\mathbf{x}}_k & = ...
  \end{alignat}
\end{subequations}

\end{document}