说明：  LTI系统的分析。用函数y=filter(p,d,x)实现差分方程的仿真，也可以用函数 y=conv(x,h)计算卷积，用y=impz(p,d,N)求系统的冲激响应，再用卷积来计算任意信号作用于系统的响应。
(Analysis of LTI systems. With the function y = filter (p, d, x) to achieve the simulation of differential equations can also be used to calculate the convolution function y = conv (x, h), with y = impz (p, d, N) seeking impulse system response, and then to calculate the convolution of any action in response to the signal system.)