l4_10
num1 = [1 -0.6 1.15 -0.98 0.98];
den1 = [1 1.27 2.02 1.54 0.98];

num2 = [2 -2.54 5 -4.3 3.27];
den2 = [1 -0.77 0.82 0.41 0.51];

%diagrama poli-zerouri
figure,
subplot(211), zplane(num1,den1)
subplot(212), zplane(num2,den2)

if isstable(num1,den1) == 1
    disp('sistem 1 stabil')
else
    disp('sistem 1 instabil')
end

if isstable(num2,den2) == 1
    disp('sistem 2 stabil')
else
    disp('sistem 2 instabil')
end

%Y = abs(X) returns the absolute value of each element in array X.
%If X is complex, abs(X) returns the complex magnitude.

poli = abs(roots(den2));
verif = 0;
for i = 1:length(poli)
    if poli(i) >= 1
        verif = 1;
        break;
    end
end

if verif == 0
    disp('stabil')
else
    disp('instabil')
end