(A,xy,'labels',labels)
full(A)
labels'

%%
% This output means that vertex 'r' is row 1, vertex 's' is row 2 and
% because A(1,2) = 1, then there is an edge between them, just like in the
% picture.
%
% One funny property is that A(2,1) = 1 too!  So we actually have to store
% each edge twice in the adjacency matrix.  This might seem wasteful, but
% its hard to avoid as I've learned while working on graph algorithms.  So
% don't worry about it!  It also makes the generalization to directed
% graphs (below) 