code: def edges_sparse(self):
          
          sparse = graph.edges_to_coo(self.edges,
                                      count=len(self.vertices))
          return sparse
docs: Edges in sparse bool COO graph format where connected
          vertices are True.
  
          Returns
          ----------
          sparse: (len(self.vertices), len(self.vertices)) bool
            Sparse graph in COO format