Hi,
Not having too many ideas, I did this: is there not a more elegant way ?
Thank you.
Fabrice
\definemathmatrix [pmatrix][matrix:parentheses][simplecommand=MATRIX]
\starttext
\startmidaligned
\startxtable[align={middle,lohi},frame=off,offset=0.8ex]
\startxrow
\startxcell
\m{P\times M=P}
\stopxcell
\startxcell
\math{\iff}
\stopxcell
\startxcell
\m{\MATRIX{x,y}\times
\MATRIX{0.22,0.78;0.53,0.47}=\MATRIX{x,y}}
\stopxcell
\stopxrow
\startxrow
\startxcell
\stopxcell
\startxcell
\m{\iff}
\stopxcell
\startxcell[align=right]
\math{\startmathcases
\NC 0.22x+0.53y=x \NR
\NC 0.78x+0.47y=y \NR
\stopmathcases}
\stopxcell
\stopxrow
\startxrow
\startxcell
\stopxcell
\startxcell
\m{\iff}
\stopxcell
\startxcell[align=right]
\m{0.78x-0.53y=0}
\stopxcell
\stopxrow
\startxrow
\startxcell
\stopxcell
\startxcell
\m{\iff}
\stopxcell
\startxcell[align=right]
\m{78x-53y=0}
\stopxcell
\stopxrow
\stopxtable
\stopmidaligned
\stoptext