Example 4.1.8 from Orfanidis
(a)

a = 0.75;
M = 14;
b = 1-a;
h = b*(a).^(0:14);
ydc = sum(h);

%Generate square wave, L = 200, period K = 50 samples
L=200;
K = 50;
n=0:L-1;
x = [mod(n,K)<K/2];

%convolve the square wave with h(n)
y = conv(h,x);
plot(n,y(1:length(n)))
hold on
plot(n,x,'--')
axis([0 200 -0.5 2.5])
xlabel('time samples')
legend('-','output','--','input')

h = [0.2 -1 2 -2 1 -0.2];
ydc = sum(h);

%Generate square wave, L = 200, period K = 50 samples
L=200;
K = 50;
n=0:L-1;
x = [mod(n,K)<K/2];

%convolve the square wave with h(n)
y = conv(h,x);
plot(n,y(1:length(n)))
hold on
plot(n,x,'--')
axis([0 200 -1.5 2.5])
xlabel('time samples')
legend('-','output','--','input')