How to remove spaces and make the sub-matrices appear larger

Question

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{makeidx}
\usepackage{graphicx}
\author{}
\begin{document}
    \[
    \left[
    \begin{array}{cccccccccccccccccccccccccccccccccccccccccccccc}
    1      & 1 & \dots                & 1 & 1                     & 1 & \dots &\dots &\dots &1            & 1  \\
    0      & 0 & \dots                & 0 & 0                     & 0 & \dots &\dots &\dots &0           & 0  \\
    \dots      & \dots & \dots                & \dots & \dots                     & \dots & \dots   &\dots &\dots &\dots          & \dots  \\
    \dots      & \dots & \dots                & \dots & \dots                     & \dots & \dots             & \dots &\dots &\dots &\dots \\
    0      & 0 & \dots                & 0 & 0                     & 0 & \dots    &\dots &\dots &0         & 0  \\
    \cline{1-11}
    &   &                      &   & \multicolumn{1}{c|}{}  &   &                        \\
    &   & \mathbf{{J^T}}    &   & \multicolumn{1}{c|}{}  &&   &&\mathbf{{A-(n-2)I}}       \\
    &   &                      &   & \multicolumn{1}{c|}{}  &   &
    \end{array} \;
    \right]
    \]
\end{document}

I have written the above code but I am having two issues:

1. There are spaces appearing inside the matrix after the dots specifically in the third last column. I don't know how to fix it.

2. Also \mathbf{{J^T}} and \mathbf{{A-(n-2)I}} are appearing very small in the matrix. Is there any way to make $J^T$ and $A-(n-2)I$ appear larger? I tried using \huge but its of no help.

Can someone kindly help me out? Thanks in advance.

Answer 1

By placing the bottom textual row in a zero-width \makebox, I could eliminate the excess space. It also allowed me to specify \Large before entering $...$ inline math mode, so as to make the text larger.

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{makeidx}
\usepackage{graphicx}
\author{}
\begin{document}
    \[
    \left[
    \begin{array}{cccccccccccccccccccccccccccccccccccccccccccccc}
    1      & 1 & \dots                & 1 & 1                     
        & 1 & \dots &\dots &\dots &1            & 1  \\
    0      & 0 & \dots                & 0 & 0                     
        & 0 & \dots &\dots &\dots &0           & 0  \\
    \dots      & \dots & \dots                & \dots & \dots    
        & \dots & \dots   &\dots &\dots &\dots          & \dots  \\
    \dots      & \dots & \dots                & \dots & \dots         
        & \dots & \dots             & \dots &\dots &\dots &\dots \\
    0      & 0 & \dots                & 0 & 0                     
        & 0 & \dots    &\dots &\dots &0         & 0  \\
    \cline{1-11}
    &   &                      &   & \multicolumn{1}{c|}{}  &   & \\
    &   & \makebox[0pt]{\Large$\mathbf{{J^T}}$}    &   & 
       \multicolumn{1}{c|}{}  &&   &&
       \makebox[0pt]{\Large$\mathbf{{A-(n-2)I}}$}      \\
    &   &                      &   & \multicolumn{1}{c|}{}  &   &
    \end{array} \;
    \right]
    \]
\end{document}

Answer 2

This is actually a two-by-two block matrix, so I'd treat it as such.

\documentclass[10pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amssymb}

\begin{document}

\[
\left[\begin{array}{cc}
\begin{matrix}
  1     & 1     & \dots & 1 \\
  0     & 0     & \dots & 0 \\
  \dots & \dots & \dots & \dots \\
  \dots & \dots & \dots & \dots \\
  0     & 0     & \dots & 0
\end{matrix}
&
\begin{matrix}
  1     & 1     & \dots & \dots & \dots & 1     & 1  \\
  0     & 0     & \dots & \dots & \dots & 0     & 0  \\
  \dots & \dots & \dots & \dots & \dots & \dots & \dots  \\
  \dots & \dots & \dots & \dots & \dots & \dots & \dots \\
  0     & 0     & \dots & \dots & \dots & 0     & 0
\end{matrix}
\\
\hline
\multicolumn{1}{c|}{\mathbf{J}^T} &
\vphantom{\begin{matrix} 0 \\ 0 \\ 0\end{matrix}} \mathbf{A}-(n-2)\mathbf{I}
\end{array}\right]
\]

\end{document}

With a phantom I force the lower part to be as high as three rows. Add rows inside it for making it higher.

Note that you don't want \mathbf{A-(n-2)I}: only “A” and “I” should be boldface.

For making the symbols in the lower part bigger, I already suggested a trick:

\newcommand{\bigentry}[2][\huge]{\begin{tabular}{@{}c@{}}#1$#2$\end{tabular}}

With this in the preamble and modifying the last part of the array into

\hline
\multicolumn{1}{c|}{\bigentry[\LARGE]{\mathbf{J}^T}} &
\vphantom{\begin{matrix} 0 \\ 0 \\ 0\end{matrix}} \bigentry[\LARGE]{\mathbf{A}-(n-2)\mathbf{I}}
\end{array}\right]

you get