accumulating a matrix (short form)
in the case one wishes to accumulate many matrices, one can default the kind of
accumulation setting the
context
to matrix, after which one can issue an arbitrary number of accumulation commands in
the short form (if one wishes to interleave with another kind of accumulation it is
sufficient to use the the normal form
xasset context m[atrix]
accumulate rmffile [arffile {instrument-dependent-args}