该因果系统的极点不全位于S 平面的左半平面，所以系统是不稳定系统。
（3）已知连续时间系统函数的极点位置分别如下所示：
试用MATLAB绘制下述6种不同情况下，系统函数的零极点分布图，并绘制响应冲激响应的时域波形，观察并分析系统函数极点位置对冲激响应时域特性的影响。 ①p=0
z = [] p = [0] k = [1]
[b,a] = zp2tf(z,p,k) sys = tf(b,a) pzmap(sys) impulse(sys)
②p=-2
z = [] p = [-2] k = [1]
[b,a] = zp2tf(z,p,k) sys = tf(b,a) pzmap(sys) impulse(sys)
③p=2
z = [] p = [2] k = [1]
[b,a] = zp2tf(z,p,k) sys = tf(b,a) pzmap(sys) impulse(sys)
④p1=2j,p2=-2j
z = [] p = [2j,-2j] k = [1]
[b,a] = zp2tf(z,p,k) sys = tf(b,a) pzmap(sys) impulse(sys) axis([0,8,-2,2])
⑤p1=-1+4j,p2=-1-4j
z = []
p = [-1+4j,-1-4j] k = [1]
[b,a] = zp2tf(z,p,k) sys = tf(b,a) pzmap(sys) impulse(sys) axis([0,6,-0.1,0.2])