如何避免坏盒子
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{bm}
\usepackage{bigdelim}
\usepackage{multirow}
\begin{document}
\begin{eqnarray*}
\bm{y} =
\begin{matrix}
\ldelim[{2}{0.1cm}& \bm{y}_{1}\ \rdelim]{2}{0.1cm}& n_1\\
& \bm{y}_{2}\ & n_2\\
\end{matrix}
,\bm{\mu} =
\begin{matrix}
\ldelim[{2}{0.1cm}& \bm{\mu}_{1}\ \rdelim]{2}{0.1cm}&n_1\\
& \bm{\mu}_{2}\ & n_2\\
\end{matrix}
\end{eqnarray*}
\begin{eqnarray*}
\Sigma =
\begin{matrix}
\ldelim[{2}{0.1cm}& \Sigma_{11} & \Sigma_{12}\ \rdelim]{2}{0.1cm}&n_1\\
& \Sigma_{21} & \Sigma_{22}\ & n_2\\
&n_1 & n_2 &\\
\end{matrix}
\end{eqnarray*}
\end{document}
%--------------------------------------------------------------
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或者我也可以使用 align*
\begin{align*}
\bm{y} =
\begin{matrix}
\ldelim[{2}{0.1cm}& \bm{y}_{1}\ \rdelim]{2}{0.1cm}&n_1\\
& \bm{y}_{2}\ & n_2\\
\end{matrix}
\quad, \bm{\mu} =
\begin{matrix}
\ldelim[{2}{0.1cm}& \bm{\mu}_{1}\ \rdelim]{2}{0.1cm}&n_1\\
& \bm{\mu}_{2}\ & n_2\\
\end{matrix}
\end{align*}
\begin{align*}
\Sigma =
\begin{matrix}
\ldelim[{2}{0.1cm}& \Sigma_{11} & \Sigma_{12}\ \rdelim]{2}{0.1cm}&n_1\\
& \Sigma_{21} & \Sigma_{22}\ & n_2\\
&n_1 & n_2 &\\
\end{matrix}
\end{align*}
但问题也会加倍。
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答案1
您正在尝试生成某种形式的边界矩阵，因此可以使用blkarray包，参见https://tex.stackexchange.com/a/346979/15925. 因此，对于最后一个例子，你可以写类似
\begin{blockarray}{ccc}
\begin{block}{[cc]c}
\Sigma_{11} & \Sigma_{12} &n_1\\
\Sigma_{21} & \Sigma_{22} & n_2\\
\end{block}
n_1 & n_2 &
\end{blockarray}
它产生一个三列均居中的对齐，由初始{ccc}选项指定，但有一个带有对齐的子矩阵{[cc]c}，这意味着前两列括在方括号中，足够大以包含该块的行。
不幸的是，你接下来会遇到一些与其余材料垂直对齐的问题。解决这些问题的一种方法是通过adjustbox：
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{blkarray,adjustbox}
\usepackage{bm}
\begin{document}
\begin{equation*}
\bm{y} =
\begin{adjustbox}{raise=-1ex} $\displaystyle
\begin{blockarray}{[c]c}
\bm{y}_{1} & n_1\\
\bm{y}_{2} & n_2
\end{blockarray} $
\end{adjustbox}
,\quad
\bm{\mu} =
\begin{adjustbox}{raise=-1ex} $\displaystyle
\begin{blockarray}{[c]c}
\bm{\mu}_{1}&n_1\\
\bm{\mu}_{2}& n_2
\end{blockarray} $
\end{adjustbox}
\end{equation*}
\begin{equation*}
\Sigma =
\begin{adjustbox}{raise=-2.5ex} $\displaystyle
\begin{blockarray}{ccc}
\begin{block}{[cc]c}
\Sigma_{11} & \Sigma_{12} &n_1\\
\Sigma_{21} & \Sigma_{22} & n_2\\
\end{block}
n_1 & n_2 &
\end{blockarray} $
\end{adjustbox}
\end{equation*}
\end{document}
答案2
首先，永远不要使用eqnarray：参见eqnarray 与 alignalign，但如果显示只有单行，则不要使用。
但是，箱子满溢是由于\ldelim和造成的\rdelim，而不是 造成的eqnarray。
在我看来，您使用的工具是错误的。
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{bm}
\begin{document}
\begin{equation*}
\bm{y} =
\begin{bmatrix}
\bm{y}_{1}\\ \bm{y}_{2}
\end{bmatrix}
\;
\begin{matrix}
n_1\\ n_2\\
\end{matrix}
,\qquad
\bm{\mu} =
\begin{bmatrix}
\bm{\mu}_{1} \\
\bm{\mu}_{2}
\end{bmatrix}
\;
\begin{matrix}
n_1\\
n_2
\end{matrix}
\end{equation*}
\end{document}
一个更复杂的宏，负责处理矩阵中更大的条目。
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{bm}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\blockcolumn}{m}
{
\seq_clear:N \l_magica_blockcolumn_index_seq
\seq_set_split:Nnn \l_magica_blockcolumn_rows_seq { \\ } { #1 }
\seq_map_inline:Nn \l_magica_blockcolumn_rows_seq
{
\seq_set_split:Nnn \l__magica_blockcolumn_temp_seq { & } { ##1 }
\seq_put_right:Nx \l_magica_blockcolumn_index_seq
{
\seq_item:Nn \l__magica_blockcolumn_temp_seq { 2 }
}
}
\hbox_set:Nn \l_magica_blockcolumn_index_box
{
$\begin{matrix}
\seq_use:Nn \l_magica_blockcolumn_index_seq { \\ }
\end{matrix}$
}
\begin{bmatrix}
\seq_use:Nn \l_magica_blockcolumn_rows_seq
{ \hspace{\dim_eval:n { -\box_wd:N \l_magica_blockcolumn_index_box-2\arraycolsep}} \\ }
\hspace{\dim_eval:n { -\box_wd:N \l_magica_blockcolumn_index_box-2\arraycolsep}}
\end{bmatrix}
}
\seq_new:N \l_magica_blockcolumn_rows_seq
\seq_new:N \l_magica_blockcolumn_index_seq
\seq_new:N \l__magica_blockcolumn_temp_seq
\box_new:N \l_magica_blockcolumn_index_box
\ExplSyntaxOff
\begin{document}
\begin{equation*}
\bm{y}=
\blockcolumn{
\bm{y}_{1} & n_1\\
\bm{y}_{2} & n_2
}
\\
,\qquad
\bm{\mu} =
\blockcolumn{
\sum\limits_{i=1}^k \bm{\mu}_{1i} & n_1\\
\bm{\mu}_{2} & n_2
}
\end{equation*}
\end{document}
