实现用SDRAM运行nios，同时用SRAM保存摄像头数据，关于神经网络控制，该函数用来计算任意函数的一阶偏导数(数值方法)。- Implemented with SDRAM run nios, while saving camera data SRAM, On neural network control, This function is used to calculate the arbitrary function of the first order partial derivativ