通过虚拟阵元进行DOA估计，滤波求和方式实现宽带波束形成，该函数用来计算任意函数的一阶偏导数(数值方法)。- Conducted through virtual array DOA estimation, Filtering summation way broadband beamforming, This function is used to calculate the arbitrary function of the first order partial derivative (numerical methods).