Question about some matrix - vector functions

[AlbFrigerio85]

Hi everyone, I'm a neofite in C++ by work and I've some questions about functions concerning Matrices and Vectors.

Let V be a column vector of length nV (i.e. nV=7) and R be a matrix of sizes Rr and Rc (i.e. Rr=10 , Rc= 18) .

What do these functions mean?
R.row (1) (I guess the first row of R)
V.resize(3)
V.resize(3,5)
R.stack(R.row (2))

Thanks everyone,
Alberto