code: def A(self):
          r
          if self._A is None:
              self._A = self.W > 0
          return self._A
docs: r"""Graph adjacency matrix (the binary version of W).
  
          The adjacency matrix defines which edges exist on the graph.
          It is represented as an N-by-N matrix of booleans.
          :math:`A_{i,j}` is True if :math:`W_{i,j} > 0`.