def move(self, u_function):
        """
        Move a mesh by using an external function which prescribes the displacement
        at any point in space.
        Useful for manipulating ``dolfin`` meshes.
        """
        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
Move a mesh by using an external function which prescribes the displacement
        at any point in space.
        Useful for manipulating ``dolfin`` meshes.