def METHOD_NAME(
        n: int, *frags: Any) -> Tuple[np.ndarray, float]:
    """
    @brief 时间步进格式为向后欧拉方法
    @param[in] n int, 表示第 `n` 个时间步（当前时间步） 
    """
    t = duration[0] + n*tau
    if n == 0:
        return uh0, t
    else:
        A = mesh.parabolic_operator_backward(tau)
        source = lambda p: pde.source(p, t)
        f = mesh.interpolate(source, intertype='node')
        f *= tau
        f += uh0
        gD = lambda p: pde.dirichlet(p, t)
        A, f = mesh.apply_dirichlet_bc(gD, A, f)
        uh0.flat = spsolve(A, f)
        solution = lambda p: pde.solution(p, t)
        e = mesh.error(solution, uh0, errortype='max')
        print(f"the max error is {e}")
        return uh0, t