%畫出Bode圖,并判斷系統閉環的穩定性
%k=2
num=2,den=[2,8,5,0];
w=logspace(-4,4,200);
[mag,phase]=bode(num,den)
grid
xlabel('Frequency[rad/sec]'),ylabel('20log(mag)[dB]')
bode(num,den)
[Gm,Pm,Wcg,Wcp]=margin(num,den)
margin(num,den)
%k=4
num=4,den=[2,8,5,0];
w=logspace(-4,4,200);
hold on 
figure(2)
[mag,phase]=bode(num,den)
grid
xlabel('Frequency[rad/sec]'),ylabel('20log(mag)[dB]')
bode(num,den)
[Gm,Pm,Wcg,Wcp]=margin(num,den)
margin(num,den)
%k=5
num=5,den=[2,8,5,0];
w=logspace(-4,4,200);
hold on 
figure(3)
[mag,phase]=bode(num,den)
grid
xlabel('Frequency[rad/sec]'),ylabel('20log(mag)[dB]')
bode(num,den)
[Gm,Pm,Wcg,Wcp]=margin(num,den)
margin(num,den)