s constant time.  There are several
disadvantages. The first is that the amount of memory used is
<i>O(V<sup>2</sup>)</i> instead of <i>O(V + E)</i> (where <i>E</i> is
the number of edges). The second is that operations that traverse all
the out-edges of each vertex (such as breadth-first search) run in
<i>O(V<sup>2</sup>)</i> time instead of <i>O(V + E)</i> time for the
adjacency list. In short, it is better to use the
<tt>adjacency_matrix</tt> for dense graphs (where <i>E</i> is close to
<i>V<sup>2</sup><