为什么方程式环境之间的分栏符会插入垂直空间？

Question

\documentclass{article}
\usepackage{lipsum}
\usepackage{multicol}
\usepackage{nccmath}
\begin{document}
    \setlength{\columnseprule}{0.4pt}
    \begin{multicols}{2}
        \begin{equation} a = a \end{equation}
        \columnbreak % why does this columnbreak insert vspace?
        \begin{equation} a = a \end{equation}
    \end{multicols}
    \begin{multicols}{2}
        \begin{equation} a = a \end{equation}
        \begin{equation} a = a \end{equation}
    \end{multicols}
\end{document}

Answer 1

您可以在本地将其设置\multicolsep为 0pt。但是，使用起来会更简单tabularx：我建议在方程环境中自动定义一个带有单元格内容的新列类型，从而使输入变得非常简单：

\documentclass{article}
\usepackage{lipsum}
\usepackage{multicol}
\usepackage{nccmath}
\usepackage{tabularx}
\makeatletter
\newcommand*{\compress}{\@minipagetrue}
\makeatother

\newcolumntype{E}{@{}>{\compress\equation}X<{\endequation}@{}}

\begin{document}
\lipsum[11]
  \setlength{\columnseprule}{0.4pt}
 {\setlength{\multicolsep}{0pt}
    \begin{multicols}{2}
        \begin{equation} a = a \end{equation}
        \columnbreak % why does this columnbreak insert vspace?
        \begin{equation} a = a \end{equation}
    \end{multicols}
    \begin{multicols}{2}
        \begin{equation} a = a \end{equation}
        \begin{equation} a = a \end{equation}
    \end{multicols}
}
\vspace{4ex}

   {\centering\belowdisplayskip=0pt
    \begin{tabularx}{\textwidth}{@{}E@{\enspace}|@{\enspace}E@{}}
    a = a & a = a \\[-1ex]
     a = a & a = a
    \end{tabularx}
}
\end{document} 

Answer 2

在前面插入一个空行\columnbreak会使其看起来相同。