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