[R] Plotting a Trivial Matrix

[Lorenzo Isella]

Dear All,
Consider a matrix (N x N) where each entry is either zero or one (can
hardly get any simpler).
Now, I would like to plot it as a 'chessboard' where every matrix entry
is a black (1) or white (0) square.
Whatever tool I use to plot it, it should not try to interpolate the
data at all.
I found some online references
http://www.phaget4.org/R/image_matrix.html
but probably I can resort to something much simpler.
Can anyone provide me with a simple example I can modify later on?
Many thanks

Lorenzo