MATLAB code for IIR Chebyshev Filter using Impulse Invariant Transform

clc;
clear all;
close all;
ap=20;
as=60;
fp=1000;
fs=3000;
fst=8000;
t=(1/fst);
wp=2*pi*fp;
ws=2*pi*fs;
w1=(2/t)*tan(wp/(2*fst));
w2=(2/t)*tan(ws/(2*fst));
[n,wn]=cheb1ord(w1,w2,ap,as,'s');
[b,a]=cheby1(n,ap,w1,'s');
[bz,az]=impinvar(b,a,fst);
freqz(bz,az,500);