These functions form different kinds of sums of the elements of
a matrix. Sum() sums the elements of a
matrix. The default is to sum all of the elements and return a
1x1 matrix. The optional parameter marg may be set to ROWS or
COLUMNS, to sum across rows or columns respectively. Setting
marg=ROWS produces a 1xc matrix of column sums. Setting
marg=COLUMNS produces an rx1 matrix of row sums.
Sumsq() functions as does Sum(), but
produces sums of squared elements.
Cusum() forms a running total across
rows. It procedes row-wise through a matrix and replaces each
element by the current accumulated total.