通过BP神经网络学习一个3维的函数的源代码，为加快速度，程序初始化的为已经经过学习的得到结点权值，如果预设为随机值，将重新学习。-BP neural network learning through a three-dimensional function of the source code for speed, the program has been initiated to study to get the node weights, if the default is a random