code: def averages(self):
          
          if not self.mesh._compute_at_vertices:
              return None
  
          return np.mean(self.vertices_per_triangle, axis=1)
docs: Access to the average of the values at the vertices for each triangle.
          If the quantities are defined at centers instead of vertices, this
          will return None.  Also see :method:`centers`.
  
          :return: numpy array or None