说明：  计算离散时间信号的DTFT 计算离散时间系统的相延迟和群延迟 计算离散时间系统的频率响应，画幅频和相频图
(Calculation of discrete-time signals in discrete-time systems DTFT calculation of the phase delay and group delay calculation of discrete-time systems frequency response, frame frequency and phase-frequency diagram)