Thanks a lot, at last it works, the trick is to assign model matrices to some
intermediary matrices, then to work on it. The code you submitted allows me to
build my matrix Z.
However, it does not seem to work with the VCV ?
I updated the rest of the code because later in the script i need to use $vcv
matrices attached to each equations. It works perfectly. In fact my doc was
out of date, sorry for the mess.
Well, merci beaucoup, and continue the good job !