%% Åîéóþóåéò äéáöïñþí
clear all
close all
b = 1;         
a = [1 0 0.81];
x = [1 zeros(1,49)];    % ä(n)
y = filter(b,a,x);      % y(n) = -0.81*y(n-2)+x(n)
figure; stem(0:49,x,'g','MarkerFaceColor',[0.75,0.75,0]);
hold on; stem(0:49,y,'x','LineWidth',2);
x=ones(1,50);           % u(n)
y = filter(b,a,x);
figure; stem(0:49,x,'g','MarkerFaceColor',[0.75,0.75,0]);
hold on; stem(0:49,y,'x','LineWidth',2);
x=[ones(1,25) zeros(1,25)];   % u(n)-u(n-25)
y = filter(b,a,x);
figure; stem(0:49,x,'g','MarkerFaceColor',[0.75,0.75,0]);
hold on; stem(0:49,y,'x','LineWidth',2);