docs: def get_simplex_solution_graph(self):
          '''
          API:
              get_simplex_solution_graph(self):
          Description:
              Assumes a feasible flow solution stored in 'flow' attribute's of
              arcs. Returns the graph with arcs that have flow between 0 and
              capacity.
          Pre:
              (1) 'flow' attribute represents a feasible flow solution. See
              Pre section of min_cost_flow() for details.
          Return:
              Graph instance that only has the arcs that have flow strictly
              between 0 and capacity.
          '''
          simplex_g = Graph(type=DIRECTED_GRAPH)
          for i in self.neighbors:
              simplex_g.add_node(i)
          for e in self.edge_attr:
              flow_e = self.edge_attr[e]['flow']
              capacity_e = self.edge_attr[e]['capacity']
              if flow_e>0 and flow_e<capacity_e:
                  simplex_g.add_edge(e[0], e[1])
          return simplex_g