docs: def neighbor_difference(self):
          """Get the euclidean distance between a node and its neighbors."""
          differences = np.zeros(self.num_neurons)
          num_neighbors = np.zeros(self.num_neurons)
  
          distance, _ = self.distance_function(self.weights, self.weights)
          for x, y in self.neighbors():
              differences[x] += distance[x, y]
              num_neighbors[x] += 1
  
          return differences / num_neighbors