# Array as a list of matrices?

I would like to have an array as a list of matrices but keep getting the error "Extra }, or forgotten \right.". As an example, I have the following:

\begin{align*}
\mathcal{X} = \left[ \left[
\begin{bmatrix}
5 & 1 & 4 & 5 \\
1 & 1 & 1 & 4 \\
5 & 3 & 1 & 4
\end{bmatrix},
\begin{bmatrix}
5 & 3 & 4 & 4 \\
2 & 5 & 3 & 4 \\
2 & 2 & 4 & 4
\end{bmatrix} \right], \left[
\begin{bmatrix}
2 & 3 & 1 & 2 \\
1 & 5 & 4 & 2 \\
3 & 4 & 5 & 3
\end{bmatrix},
\begin{bmatrix}
2 & 3 & 1 & 4 \\
4 & 4 & 2 & 1 \\
4 & 1 & 1 & 1
\end{bmatrix} \right], \\ \left[
\begin{bmatrix}
5 & 5 & 4 & 3 \\
5 & 1 & 4 & 2 \\
1 & 2 & 1 & 2
\end{bmatrix},
\begin{bmatrix}
5 & 1 & 4 & 1 \\
3 & 1 & 5 & 4 \\
5 & 4 & 2 & 3
\end{bmatrix} \right] \right]
\end{align*}


but the final bracket will not be printed on the screen. This is shown here

Is there a way of making the bracket appear or better yet, doing this in a more organized way? I have tried \Biggr[ but the bracket is not of the same size. Likewise I have tried creating more matrices but has similarly not worked. Thanks.

• Welcome to TeX.SX! \left and \right cannot straddle a line break in a display alignment. Commented Dec 28, 2022 at 22:45

\left and \right cannot straddle two lines in an alignment display.

In this case you can match the opening \left[ with \right. and do similarly in the second line.

\documentclass{article}
\usepackage{amsmath}
\usepackage{showframe}% just to see the page margins

\begin{document}

\begin{align*}
\mathcal{X} =
% outer
\left[
\left[
\begin{bmatrix}
5 & 1 & 4 & 5 \\
1 & 1 & 1 & 4 \\
5 & 3 & 1 & 4
\end{bmatrix},
\begin{bmatrix}
5 & 3 & 4 & 4 \\
2 & 5 & 3 & 4 \\
2 & 2 & 4 & 4
\end{bmatrix}
\right],
\left[
\begin{bmatrix}
2 & 3 & 1 & 2 \\
1 & 5 & 4 & 2 \\
3 & 4 & 5 & 3
\end{bmatrix},
\begin{bmatrix}
2 & 3 & 1 & 4 \\
4 & 4 & 2 & 1 \\
4 & 1 & 1 & 1
\end{bmatrix}
\right],
\right. % match with \left[
\\
\left.
\left[
\begin{bmatrix}
5 & 5 & 4 & 3 \\
5 & 1 & 4 & 2 \\
1 & 2 & 1 & 2
\end{bmatrix},
\begin{bmatrix}
5 & 1 & 4 & 1 \\
3 & 1 & 5 & 4 \\
5 & 4 & 2 & 3
\end{bmatrix}
\right]
\right]
\end{align*}

\end{document}


Remove showframe that's used here just to see that the alignment fits.

An alternative version:

\documentclass{article}
\usepackage{amsmath}
\usepackage{showframe}% just to see the page margins

\begin{document}

\begin{align*}
\mathcal{X} =
% outer
\left[ \vphantom{\begin{matrix}0\\0\\0\end{matrix}}\right.
& \left[
\begin{bmatrix}
5 & 1 & 4 & 5 \\
1 & 1 & 1 & 4 \\
5 & 3 & 1 & 4
\end{bmatrix},
\begin{bmatrix}
5 & 3 & 4 & 4 \\
2 & 5 & 3 & 4 \\
2 & 2 & 4 & 4
\end{bmatrix}
\right],
\\
& \left[
\begin{bmatrix}
2 & 3 & 1 & 2 \\
1 & 5 & 4 & 2 \\
3 & 4 & 5 & 3
\end{bmatrix},
\begin{bmatrix}
2 & 3 & 1 & 4 \\
4 & 4 & 2 & 1 \\
4 & 1 & 1 & 1
\end{bmatrix}
\right],
\\
& \left[
\begin{bmatrix}
5 & 5 & 4 & 3 \\
5 & 1 & 4 & 2 \\
1 & 2 & 1 & 2
\end{bmatrix},
\begin{bmatrix}
5 & 1 & 4 & 1 \\
3 & 1 & 5 & 4 \\
5 & 4 & 2 & 3
\end{bmatrix}
\right]
\left.\vphantom{\begin{matrix}0\\9\\9\end{matrix}}\right]
\end{align*}

\end{document}