表格第一行的额外垂直空间

Question

代码如下所示。当第一行不包含特殊单元格（一个单元格中有两行）时，这种情况实际上不会发生。但我不太清楚如何修复它。

\documentclass[12pt]{article}
\usepackage{amsmath}
\renewcommand*{\arraystretch}{1.3}
\usepackage{graphicx}
\usepackage{xspace}
\usepackage{tabu} % tabular
\usepackage{multirow} % tables
\usepackage{setspace}
\onehalfspacing % or \doublespacing
\newcommand{\specialcell}[2][c]{\begin{tabu}[#1]{@{}c@{}}#2\end{tabu}} % two lines in a table cell 
\tabulinesep=1.8mm % tabu vertical spacing/need {tabu} package

\begin{document}

\begin{table}[htbp]
    \begin{tabu}{cccccc}
    \hline
    & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb}\\
    \hline
    a & a & a & a & a & a\\
    \hline 
    b & b & b & b & b & b\\ 
    \hline 
    c & c & c & c & c & c\\ 
    \hline 
    \end{tabu}
\end{table}

\end{document}

Answer 1

这里我只是重新定义了\specialcell使用堆栈，而不是tabu。

\documentclass[12pt]{article}
\usepackage{amsmath}
\renewcommand*{\arraystretch}{1.3}
\usepackage{graphicx}
\usepackage{xspace}
\usepackage{tabu} % tabular
\usepackage{multirow} % tables
\usepackage{setspace}
\onehalfspacing % or \doublespacing
%\newcommand{\specialcell}[2][c]{\begin{tabu}[#1]{@{}c@{}}#2\end{tabu}} % two lines in a table cell 
\tabulinesep=1.8mm % tabu vertical spacing/need {tabu} package
\usepackage[usestackEOL]{stackengine}
\newcommand\specialcell[2][c]{\Centerstack[#1]{#2}}
\begin{document}

\begin{table}[htbp]
    \begin{tabu}{cccccc}
    \hline
    & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb} & \specialcell{aaa\\bbb}\\
    \hline
    a & a & a & a & a & a\\
    \hline 
    b & b & b & b & b & b\\ 
    \hline 
    c & c & c & c & c & c\\ 
    \hline 
    \end{tabu}
\end{table}

\end{document}

堆栈的基线跳跃可以通过以下方式更改，例如，声明

\setstackgap{L}{22pt}

导致