Hello,
This is just for discussion. I used to think that in doing mathematical calculations, the matrices need not to be mixed up with series. For the sake of clarity one can not, let's say multiply a series by a matrix. Is that right?
Well, in the following script this kind of multiplication works fine. Is that normal -- I mean, an intentionnally built feature -- or should we avoid such a mixed operation?

nulldata 100
series x1 = normal()
matrix unit = ones($nobs,1)
scalar prod = unit'*x1      # matrix * series

matrix mx1 = x1
scalar prod = unit'*mx1     # matrix * matrix

best,
artur