In the course of some recent experimentation I found it useful to
have a built-in function to "flatten" an array of matrices to one
big matrix, and I enabled such a function in my working copy of the
gretl sources.
The function in question takes as argument 1 an array of matrices
and as argument 2 either "hcat" or "vcat": in the hcat case the
member matrices are concatenated horizontally (which requires that
they all have the same number of rows); under vcat they're
concatenated vertically (requiring a common number of columns). In
either case a hansl function could be written quite easily to do the
job, but a built-in function is likely a good deal faster.
Anyway, my particular need for this function has passed but I was
wondering if others would find it useful. If so I can add it to git,
if not I'll quietly retire it.
Allin