clc
clear all
close all
omegac2=0.3*pi;Apmax=1;
Armin=60;
omegar1=0.35*pi;
T=1;
wp=[omegac2/pi];wr=[omegar1/pi];
[N,Wc]=buttord(wp,wr,Apmax,Armin);
[b,a]=butter(N,Wc,'low');
w=linspace(0,1*pi,500);
H=freqz(b,a,w);
mag=20*log10(abs(H+eps));
plot(w/pi,mag);axis([0,2,-110,5]);grid;
set(gca,'ytick',[(-100:20:-20),-3,0])
set(gca,'xtick',[(0:0.2:0.4),0.50,(0.6:0.1:2)]);
sys=tf(b,a,T);