Postby gawrilow » 20 Jun 2013, 20:07
row(i) gives you a selected row represented by an object with Vector-like interface, that is, access to a single element there is provided via operator[]. The same for columns: col(j) returns something behaving like a Vector. The following four expressions are functionally equivalent:
m[j] m.row(i)[j] m.col(j) m(i,j)
The last one is the most efficient, because it does not create any temporary intermediate objects.