def METHOD_NAME(self, uh, timeline):
    '''  piccard 迭代  向后欧拉方法 '''
    t1 = timeline.next_time_level()
    i = timeline.current
    dt = timeline.current_time_step_length()
    A = self.get_current_left_matrix(timeline)
    F = self.get_current_right_vector(uh, timeline)
    A0, b = self.apply_boundary_condition(A, F, uh, timeline)
    e = 0.000000001
    error = 1
    xi_new = self.space.function()
    xi_new[:] = copy.deepcopy(uh[:,i])
    while error > e:
        xi_tmp = copy.deepcopy(xi_new[:])
        R = self.nr.robin_bc(A, xi_new, lambda x,
                n:self.pde.boundary_nonlinear_robin(x, n, t1),
                threshold=self.pde.is_robin_boundary())
        r = self.M@uh[:, i] + dt*b
        R = self.M + dt*R
        xi_new[:] = spsolve(R, r).reshape(-1)