Elevation-fitting

代码说明：

  BP 网络具有以任意精度逼近定义在紧致子集上的任意非线性函数的能力, 因而被广泛应用于识别、预测、拟合。(BP network has to approach any degree of accuracy defined in the compact subset of the capacity of any nonlinear function, which is widely used in identification, prediction, fit.)