Doing block matrices with array environment

Question

I am used to writing block matrices using the array environment, when these matrices are decomposed in four blocks, controlling vertical spacing and using \hfill, etc.. Now I wanted to draw a matrix decomposed in nine blocks, but the vertical lines made by the array environment broke up. How can I fix it without completely changing the approach? (say, I'm not interested in solutions using tikz, at least for now).

Here's a MWE (done in Overleaf):

\documentclass[a4paper]{article}
\usepackage[english]{babel}
\usepackage[utf8x]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[a4paper,top=3cm,bottom=2cm,left=3cm,right=3cm,marginparwidth=1.75cm]{geometry}
\usepackage{amsmath}
\usepackage{graphicx}



\begin{document}

\[  \left(
    \begin{array}{c|c}
      \mbox{\large $0$} &  \mbox{\large ${\rm Id}_n$} \\[.7ex] \hline \\[-1.5ex]
      \mbox{\large $-{\rm Id}_n$} & \mbox{\large $0$}\\
    \end{array}
  \right) \qquad \left(
    \begin{array}{c|c|c}  
\mbox{\large $0$} & \mbox{\large $0$} & \mbox{\large $0$} \\[.7ex] \hline \\[-1.5ex]
    \mbox{\large $0$} &  \mbox{\large $0$} &  \mbox{\large ${\rm Id}_n$} \\[.7ex] \hline \\[-1.5ex]
      \mbox{\large $0$} & \mbox{\large $-{\rm Id}_n$} & \mbox{\large $0$}\\
    \end{array}
  \right). \]
\end{document}

Thanks!

Answer 1

Instead of doing \large in every cell, do it globally for the array. Don't use \\ after \hline.

\documentclass[a4paper]{article}
\usepackage{amsmath}

\begin{document}

\[
\left(
  \mbox{\large$
    \renewcommand{\arraystretch}{1.2}
    \begin{array}{c|c}
    0 & \mathrm{Id}_n \\
    \hline
    -\mathrm{Id}_n & 0 \\
    \end{array}
  $}% end of \mbox
\right)
\qquad
\left(
  \mbox{\large$
    \renewcommand{\arraystretch}{1.2}
    \begin{array}{c|c|c}  
    0 & 0 & 0 \\
    \hline
    0 & 0 & \mathrm{Id}_n \\
    \hline
    0 & -\mathrm{Id}_n & 0 \\
    \end{array}
  $}% end of \mbox
\right).
\]
\end{document}

I removed all unnecessary packages. Don't use utf8x for it's been unmaintained for several years, but utf8. Note also that \rm has been deprecated for more than 20 years.