说明：  将xi，x2作为RBF网络的输入数据，将y作为RBF网络的输出数据，分别建立近似和精确RBF网络进行回归分析，并评价网络拟合效果。
(Xi, X2 as the input data of RBF network, y as the output data of RBF network, respectively establish approximate and accurate RBF network for regression analysis, and evaluate the network fitting effect.)