b = [1]; a = [1, -1, 0.9]; n = [-20:120];

h = impz(b,a,n);

set(gcf,'Color','white');

%subplot(2,1,1);

stem(n,h); title('Impulse Response');

xlabel('n'); ylabel('h(n)'); grid on;

x = stepseq(0,-20, 120); s = filter(b,a,x);

figure; set(gcf,'Color','white');

%subplot(2, 1,2);

stem(n,x); title('Step Sequence');

xlabel('n'); ylabel('x(n)'); grid on;

figure; set(gcf,'Color','white');

%subplot(2, 1,2);

stem(n,s); title('Step Response');

xlabel('n'); ylabel('s(n)'); grid on;