clear
% close all

a = [1,-1,0.9];
b = [1];

%a = [1, -3, -4];
%b = [1, 2];

n = -20:120;

h = impz(b,a,n);
figure(1)
stem(n,h);

x = stepseq(0,-20,120);
s = filter(b,a,x);
figure(2)
subplot(2,1,1)
stem(n,x)
subplot(2,1,2)
stem(n,s)

sum_h = sum(abs(h))

z = roots(a)

z = z + 1i*0.000000000000000000001;

figure(3)
clf
plot(z,'*')

angle = 0:2*pi/100:2*pi;          % vector of angles at which points are drawn
R = 1;                            % Unit radius

uc = R*exp(1i*angle);
figure(3)
hold on
plot(uc,'.')

axis equal;
grid on