零相移滤波器m函数，优点是克服了滤波器产生的相位滞后，缺点是本仿真不能保证实时性，其原理为输入一次序列，正反各变换一遍。-Zero phase shift filter m function, the advantages of the filter to overcome the phase lag, the disadvantage is that the simulation can not guarantee real-time, the principle of the input s