code: def move(self, u_function):
          
          if self.mesh:
              self.u = u_function
              delta = [u_function(p) for p in self.mesh.coordinates()]
              movedpts = self.mesh.coordinates() + delta
              self.polydata(False).GetPoints().SetData(numpy_to_vtk(movedpts))
              self.poly.GetPoints().Modified()
              self.u_values = delta
          else:
              colors.printc("Warning: calling move() but actor.mesh is", self.mesh, c=3)
          return self
docs: Move a mesh by using an external function which prescribes the displacement
          at any point in space.
          Useful for manipulating ``dolfin`` meshes.