adopt gauss package (with tikz)

Question

since I'm missing the ability to pass some kind of "format"-string to the gmatrix environment of the gauss package, and I learnt that this is not possible with redefining some environemnts used by the gauss package (see gauss package set formatting (like the option for the array env)), I finally came to the point, when I decided to emulate some parts of the behaviour of the gauss package to be more flexible.

I just wanted to ask you if there is some way to attach tikz arrows onto elements of the array environment (and thus the pmatrix environment of the amsmath package) or if the only way to do something like this is by setting the whole array/matrix within tikz?

(If maybe someone has already done this (then I'd be glad if this one would share ;) ))

Answer 1

The package nicematrix provides environments {NiceArray}, {NiceMatrix}, {pNiceMatrix}, etc. similar to the environments of array and amsmath but with the creation of a PGF/Tikz nodes under the cells of the array.

It's possible to use these nodes with Tikz after the construction of the array.

\documentclass{article}    
\usepackage{nicematrix,tikz}    
\begin{document}
$\begin{bNiceMatrix}
1 & 2 & 3 \\
4 & 5 & 6 \\
7 & 8 & 9 
\CodeAfter
\tikz \draw (1-3.east)  -- ++ (3mm,0) node [anchor = west]{\tiny $-3$} |- (2-3.east) ; 
\end{bNiceMatrix}$    
\end{document}