Butterfly 2

%butterworth filter - impulse invariance
clc;clear all; close all;
[nb,wb]=buttord(0.2*pi,0.3*pi,1,15,'s');
[b,a]=butter(nb,wb,'s');
sys=tf(b,a);
bode(sys);
figure;
[num1 den1]=impinvar(b,a,1);
freqz(num1,den1)
HZ=tf(num1,den1,1)