%Matlab Program 1-18
disp('Create system model')
sys=tf([1 11 36 26],[1 14.6 74.96 153.7 99.65]);
sys=zpk(sys)
disp('A lalanced state - space realization')
[sysb,gram]=balreal(sys);
gram

disp('Check the states that cab removed')
disp('Reduce the model to lower order')
sysr=modred(sysb,3:4,'mod');
sysr=zpk(sysr)

%compare the original system to the reduced system
step(sys,'r-')
grid