x=[0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1]
y=filter(b,a,x)
figure(1),stem(0:length(x)-1,x),grid
figure(2),stem(0:length(y)-1,y),grid