Problem with vertical alignmentof in table's environment "Tabu"

Question

I need your help for this problem. Since a year ago, I'm using LaTeX for wirite a math handbook. From them until now, I've had a few problems but with this forum i have solve them. But now, I can't solve my lastest problem.

Recently, I bought a new computer and I reinstalled the lastest MiKTeX full installation and TexMaker. And when I added new code and I've compiled for my handbook, I obtained the next unpleasant result.

https://i.sstatic.net/grDAo.jpg

The code compilated are the following:

\begin{table}[H]
\begin{tabu}{cX[m]}
$\mathbf{C}=\begin{pmatrix}
a_{11}&a_{12}&\cdots&a_{1n}\\
a_{21}&a_{22}&\cdots&a_{2n}\\
\vdots&\vdots&\ddots&\vdots\\
a_{n1}&a_{n2}&\cdots&a_{nn}\\
\end{pmatrix}$&La dimensión de una matriz cuadrada es, por tanto, $n\times n$. 
Sin embargo, es mucho más usual decir que una matriz cuadrada \textbf{es de orden $n$}.
Por ejemplo, la matriz $\bf C$ es de orden $n$ (${\bf C}\in\mathbb{M}_{\,n\times n\,}$)
y la matriz $\bf D$ es de orden $4$ (${\bf D}\in\mathbb{M}_{\,4\times 4\,}$).
Dentro de este tipo de matrices cabe destacar dos elementos
\underline{exclusivos de las matrices cuadradas}: las \textbf{diagonales}.\\
\end{tabu}
\end{table}

As you can see, the text and the mathematical environment (the matrix) are not aligned and not centered, too. Which is what I want to achieve.

Also, this problem happens to me when I changed the computer: with my old notebook, the matrix and the text are perfectly aligned. The result was similar to the following:

https://i.sstatic.net/uoQ8t.jpg

This I have achieved with the following code:

\begin{table}[H]
\begin{tabular}{cm{\linewidth}}
$\mathbf{C}=\begin{pmatrix}
a_{11}&a_{12}&\cdots&a_{1n}\\
a_{21}&a_{22}&\cdots&a_{2n}\\
\vdots&\vdots&\ddots&\vdots\\
a_{n1}&a_{n2}&\cdots&a_{nn}\\
\end{pmatrix}$&La dimensión de una matriz cuadrada es, por tanto, $n\times n$. 
Sin embargo, es mucho más usual decir que una matriz cuadrada \textbf{es de orden $n$}.
Por ejemplo, la matriz $\bf C$ es de orden $n$ (${\bf C}\in\mathbb{M}_{\,n\times n\,}$)
y la matriz $\bf D$ es de orden $4$ (${\bf D}\in\mathbb{M}_{\,4\times 4\,}$).
Dentro de este tipo de matrices cabe destacar dos elementos
\underline{exclusivos de las matrices cuadradas}: las \textbf{diagonales}.\\
\end{tabular}
\end{table}

But the text overflows from the page. Is there any order, command or package to adjust the m type column to the end the page and avoid the overflow?

Thanks! And sorry for my horrific english!

Answer 1

i would not use tabu ... after recent changes in the package array is has one "bug" more: columns of the type m doesn't work anymore as expected.

better is used `tabularx:

\documentclass[12pt,a4paper]{article}
\usepackage{amsmath, amssymb}
\usepackage{tabularx}

%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%

\begin{document}
    \begin{table}[htb]
\renewcommand\tabularxcolumn[1]{m{#1}}
\begin{tabularx}{ \linewidth}{@{}
                            >{\hsize=0.8\hsize}X
                            >{\hsize=1.2\hsize}X
                              @{}
                              }
\[
\mathbf{C}=\begin{pmatrix}
            a_{11}  & a_{12}    &\cdots & a_{1n}\\
            a_{21}  & a_{22}    &\cdots & a_{2n}\\
            \vdots  & \vdots    &\ddots & \vdots\\
            a_{n1}  & a_{n2}    &\cdots & a_{nn}\\
            \end{pmatrix}
\]
    & La dimensión de una matriz cuadrada es, por tanto, $n\times n$.
Sin embargo, es mucho más usual decir que una matriz cuadrada \textbf{es de orden $n$}.
Por ejemplo, la matriz $\mathbf{C}$ es de orden $n$ ($\mathbf{C}\in\mathbb{M}_{\,n\times n\,}$)
y la matriz $\mathbf{D}$ es de orden $4$ ($\mathbf{D}\in\mathbb{M}_{\,4\times 4\,}$).
Dentro de este tipo de matrices cabe destacar dos elementos
\underline{exclusivos de las matrices cuadradas}: las \textbf{diagonales}.\\
\end{tabularx}
\end{table}
\end{document}

(red lines indicate text border)