说明：  进行波形数据分析,语音信号的采集与处理，数字信号处理课设，该函数用来计算任意函数的一阶偏导数(数值方法)。
( Waveform data analysis, Acquisition and Processing of the speech signal, digital signal processing class-based, This function is used to calculate the arbitrary function of the first order partial derivative (numerical methods).)