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I am trying to make a matrix with external elements and dashed separation lines for clarification. I have gotten pretty far using the blkarray package. However, I have failed to add a horizontal separation line between rows f and g, only inside the matrix. Also, I would like the separation lines to be dashed.

EDIT:
Sorry, I should have been more explicit. I would like both separation lines to be dashed. Will try no if this works with any of the provided answers.

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\documentclass{article} \usepackage{amsmath} \usepackage{blkarray} \begin{document} \begin{equation} H = \begin{blockarray}{ccccc} & a & b & c & d\\ \begin{block}{c(cc|cc)} e & 1 & 2 & 3 & 4\\ f & 5 & 6 & 7 & 8\\ g & 9 & 0 & 1 & 2\\ h & 3 & 4 & 5 & 7\\ \end{block} \end{blockarray} \end{equation} \end{document}
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With {pNiceArray} of nicematrix.

\documentclass{article} \usepackage{nicematrix} \begin{document} \begin{equation} H = \begin{pNiceArray}{cc|cc}[first-row,first-col] & a & b & c & d\\ e & 1 & 2 & 3 & 4\\ f & 5 & 6 & 7 & 8\\ \hdottedline g & 9 & 0 & 1 & 2\\ h & 3 & 4 & 5 & 7\\ \end{pNiceArray} \end{equation} \end{document}

You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).

Ouput of the above code

If you want dashed lines, you can draw them with Tikz, you can define a custom type of line with custom-line which provides a way to use whatever Tikz style of line you want. You need at least nicematrix version 6.10a (2022-06-26).

\documentclass{article} \usepackage{nicematrix,tikz} \begin{document} \NiceMatrixOptions { custom-line = { letter = I , % <- for the vertical rules command = hdashedline , % <- for the horizontal rules tikz = dashed , total-width = \pgflinewidth % <- optional } } \begin{equation} H = \begin{pNiceArray}{ccIcc}[first-row,first-col] & a & b & c & d\\ e & 1 & 2 & 3 & 4\\ f & 5 & 6 & 7 & 8\\ \hdashedline g & 9 & 0 & 1 & 2\\ h & 3 & 4 & 5 & 7\\ \end{pNiceArray} \end{equation} \end{document}

Output of the above code

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  • Ok, here I can easily make the vertical line dotted by replacing cc|cc with cc:cc. Any suggestions of how I could turn those dotted lines into dashed lines? Commented Feb 16, 2022 at 11:16
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Use \BAhhline with ~ column:

\documentclass{article} \usepackage{amsmath} \usepackage{blkarray} \begin{document} \begin{equation} H = \begin{blockarray}{ccccc} & a & b & c & d\\ \begin{block}{c(cc|cc)} e & 1 & 2 & 3 & 4\\ f & 5 & 6 & 7 & 8\\ \BAhhline{~..|..} g & 9 & 0 & 1 & 2\\ h & 3 & 4 & 5 & 7\\ \end{block} \end{blockarray} \end{equation} \end{document}

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