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I want to put a matrix in a matrix, more precisely what I wanna reach is basically this:

enter image description here

I'm using the pmatrix-environment. How can I do this?

Edit: Sorry, I wasn't precise - what I actually wanna do, is replacing the a's here by a matrix A which is aligned in the middle of the 4 rows and the 5 columns. The example above seems to be easier since the number of rows/columns of A_1 is odd.

\[
\begin{pmatrix}
a & a & a & a & 1 \\
a & a & a & a & 2 \\
a & a & a & a & 3 \\
a & a & a & a & 4 \\
\end{pmatrix}
\]
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4
  • 1
    you should show what you tried, and if it has an error someone could fix, there doesn't seem to be anything special needed simply use \vdots & A_{1} as the third row, you may think of it as a nested matrix but TeX doesn't need to know that
    – David Carlisle
    Jan 11, 2020 at 12:25
  • The picture above is from a book, not from me. I didn't try anything because I don't know how.... but yes, your hint works, thanks. How would I do it if I wanted only one column (the right one) in the matrix and the A_1 to stand for a 4x4 matrix on the left of the column?
    – ATW
    Jan 11, 2020 at 12:30
  • you could still have made a test document even if it just has a basic pmatrix, I am not sure I understand your second request but perhaps make the first row be * & \cdots & * then you can make the later row A_1 & & so the A comes under the left *
    – David Carlisle
    Jan 11, 2020 at 12:34
  • I edited the question.
    – ATW
    Jan 11, 2020 at 12:43

2 Answers 2

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2

Nest matrix inside pmatrix:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
\begin{pmatrix}
\alpha_{11} & \begin{matrix} * & \dots & * \end{matrix} \\
\begin{matrix} 0 \\ \vdots \\ 0 \end{matrix} & A_{11}
\end{pmatrix}
\]

\end{document}

enter image description here

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3

Like this?

enter image description here

With use of the nicematrix package:

\documentclass[margin=3mm]{standalone}
\usepackage{bm}
\usepackage[table]{xcolor}
\usepackage{nicematrix}

\begin{document}
$
\begin{pNiceArray}{CCCC}
\alpha_{11} &   *   &   \dots   &   *   \\
0           &   \Block{3-3}<\huge\bm>{A_1} 
                    &           &       \\
\vdots      &       &           &       \\
0           &       &           &       
\end{pNiceArray}
$
\end{document}

or

enter image description here

\documentclass[margin=3mm]{standalone}
\usepackage{bm}
\usepackage{nicematrix}

\begin{document}
$
\begin{pNiceArray}{CCCC}
\alpha_{11} &   *   &   \Cdots   &   *   \\
0           &   \Block{3-3}<\huge\bm>{A_1} 
                    &           &       \\
\Vdots      &       &           &       \\
0           &       &           &       
\end{pNiceArray}
$
\end{document}

Shoved result you will obtain after two compilation of above MWE.

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