[num,den]=butter(6,1000,'s');
lpass=tf(num,den);
%bode(lpass)

[num,den]=butter(6,2000,'high','s');
hpass=tf(num,den);
%bode(hpass)

[num,den]=butter(6,[1000 2000],'stop','s');
bstop=tf(num,den);
%bode(bstop)

[num,den]=butter(6,[1000 2000],'s');
bpass=tf(num,den);
%bode(bpass)

[num,den]=butter(4,0.9,'s');
lpass=tf(num,den);

t=[0:.01:100]';'
freq=5;
input=cos(2*pi*freq/100*t);
ol20=lsim(lpass,input,t);
plot(t,ol20,t,input)
disp('frequency 5')
pause
input=sign(cos(2*pi*freq/100*t));
ol20=lsim(lpass,input,t);
plot(t,ol20,t,input)
disp('frequency 5')
pause
freq=2;
input=sign(cos(2*pi*freq/100*t));
ol20=lsim(lpass,input,t);
plot(t,ol20,t,input)
disp('frequency 2')
pause
freq=10;
input=sign(cos(2*pi*freq/100*t));
ol20=lsim(lpass,input,t);
plot(t,ol20,t,input)
disp('frequency 10')
pause
freq=30;
input=sign(cos(2*pi*freq/100*t));
ol20=lsim(lpass,input,t);
plot(t,ol20,t,input)
axis([0 100 -1.5 1.5])
disp('frequency 30')
pause