Fabrice Couvreur schrieb am 14.10.18 um 10:46:

Hi,
I tried to use Metafun and \definemathmatrix [pmatrix] [matrix: parentheses] [simplecommand = MATRIX] to create two matrices, but that does not work.

1. You have a space in [matrix: parentheses]

2. When you have only simple graphics like in your example you can use framed.

\starttext

\startformula
A\,
\startmathmatrix[left=\left(,right=\right)]
\NC \framed[width=1em,height=1em,frame=off,bottomframe=on]{} \NC \framed[width=1em,height=1em,frame=off,bottomframe=on,leftframe=on]{} \NR
\NC \framed[width=1em,height=1em,frame=off,rightframe=on]{} \NC \framed[width=1em,height=1em]{} \NR
\stopmathmatrix
\stopformula

\stoptext

Wolfgang