ef="using_adjacency_list.html#sec:adjacency-list-properties">interior
properties</a>. The types of all property values must be
Copy Constructible, Assignable and Default Constructible.

In the case of an undirected graph, the
<tt>adjacency_matrix</tt>. class does not use a full <i>V x V</i>
matrix but instead uses a lower triangle (the diagonal and below)
since the matrix for an undirected graph is symmetric. This reduces
the storage to <i>(V<sup>2</sup>)/2</i>.  <a
href="#fig:undir-adj-matrix-graph">Figure