%% (1) compute impulse response h and plot
n = 0:100;
a = [1 -0.5 0.25]; % left hand side coefficients
b = [1 2 1]; % right hand side coefficients
h = filter(b,a,[1,zeros(1,length(n)-1)]); % impulse response
plot(n,h),xlabel('n'),ylabel('impulse response, h(n)'),grid on

%% (2) stability -> test if the system is absolutely summable
if sum(abs(h))<Inf
disp('System is stable')
else
disp('System is unstable')
end