4

I created a matrix by this code

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
A_{n+1}=
 \begin{pmatrix}
    a & \begin{tabular}{ccccc}
           0 & 0 & \ldots & 0 & 0 \\
        \end{tabular} 
    & 1\\
 \begin{tabular}{c}
    0\\
    \vdots\\
 \end{tabular} & A_n
               & \begin{tabular}{c}  0\\
                   \vdots
                 \end{tabular}  
  \\
  1 & \begin{tabular}{ccccc}
  0 & 0 & \ldots & 0 & 0 \\
\end{tabular} & a\\
\end{pmatrix}
\]
\end{document}

But I don't like the result because the margin between the "a" and the first "0" in the first line is too large. I guess it's due to the tabular environment. Anyway to improve it?

enter image description here

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  • Already the great egreg provided the best answer, but just give @{} will produce almost the same output of egreg suggestion, and the code is \begin{tabular}{@{}c@{}} Commented 2 hours ago

1 Answer 1

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7

You want a matrix, not a tabular.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
A_{n+1}=
\begin{pmatrix}
  a & \begin{matrix} 0 & 0 & \ldots & 0 & 0 \end{matrix} & 1 \\
  \begin{matrix} 0 \\ \vdots \end{matrix} & A_n \\
  1 & \begin{matrix} 0 & 0 & \ldots & 0 & 0 \end{matrix} & a
\end{pmatrix}
\]

\end{document}

output

Easier with nicematrix:

\documentclass{article}
\usepackage{amsmath}
\usepackage{nicematrix}

\begin{document}

\[
A_{n+1}=
\begin{pNiceMatrix}
  a & 0 & 0 & \dots & 0 & 0  & 1 \\
  0 & \Block{2-5}{A_n} \\
  \vdots  \\
  1 & 0 & 0 & \dots & 0 & 0  & a
\end{pNiceMatrix}
\]

\end{document}
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