% Program P2_8
% Stability test based on the sum of the absolute 
% values of the impulse response samples
clf;
num = [1 -0.8]; den = [1 1.5  0.9];
N = 200;
h = impz(num,den,N+1);
parsum = 0;
for k = 1:N+1;
	parsum = parsum + abs(h(k));
	if abs(h(k)) < 10^(-6), break, end
end
% Plot the impulse response
n = 0:N;
stem(n,h)
xlabel('Time index n'); ylabel('Amplitude');
% Print the value of abs(h(k)) 
disp('Value =');disp(abs(h(k)));