[Tex/LaTex] overfull hbox (pt too wide) in paragraph at lines in eqnarray*

equations

How can I avoid the bad box 

\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}

%—————————————————————

Overfull \hbox (4.68791pt too wide) in paragraph at lines 12--12
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 17--17
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 17--17
[]|$[]$|

Or I can also use 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*}

However, the problems will be doubled.

Overfull \hbox (6.11073pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (6.11073pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (6.11073pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (6.11073pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 21--21
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 29--29
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 29--29
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 29--29
[]|$[]$|  

Overfull \hbox (4.68791pt too wide) in paragraph at lines 29--29
[]|$[]$|

Best Answer

You are trying to produce some form of bordered matrix and so could use the blkarray package, cf. https://tex.stackexchange.com/a/346979/15925 . So for the final example you would write something like

\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}

which produces an alignment with three columns all centered, specified by the initial {ccc} option, but has a submatrix with alignment {[cc]c}, meaning the first two columns are enclosed in square brackets, large enough to enclose the rows of that block.

Unfortunately, you then run in to some vertical alignment problems with the rest of the material. One way to fix these is via adjustbox:

Sample output

\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}
Related Question