%unstable.m
clear;close all
N = 256
n = [0:N-1].';
k = [0:N-1].';
f = [0:N-1].'/N;
delta = [1;zeros(N-1,1)];

b = 1
a = [1; -0.9]
figure
subplot(2,1,1);bar(n,delta);axis tight
h = filter(b,a,delta);
subplot(2,1,2);bar(n,h);axis tight

b = 1
a = [1; -1.1]
figure
subplot(2,1,1);bar(n,delta);axis tight
h = filter(b,a,delta);
subplot(2,1,2);bar(n,h);axis tight

b = 1
a = [1; 0.9]
figure
subplot(2,1,1);bar(n,delta);axis tight
h = filter(b,a,delta);
subplot(2,1,2);bar(n,h);axis tight

b = 1
a = [1; 1.1]
figure
subplot(2,1,1);bar(n,delta);axis tight
h = filter(b,a,delta);
subplot(2,1,2);bar(n,h);axis tight

