A Function Fitting Method Data $(p_i,a_i) \in \mathbb{T}^m\times\{-1,1\}$, $i = 1,2,...n$. Let $C_{\lambda}(f) = \sum\limits_{i=1}^{n}(f(p_i)-a_i)^2 + \|f\|_{L^2}^2 + \lambda\|\nabla^kf\|_{L^2}^2$ where $\nabla^kf = (\frac{\partial^k{f}}{\partial{x_1}},\frac{\partial^k{f}}{\partial{x_2}},...\fr...