% ex6_3
% 繪制超前校正環節的頻率特性
figure('pos',[50,50,400,150],'color','w');
alpha=0.2;
T=10;
G=tf([alpha*T alpha],[alpha*T 1]);
a1=axes('pos',[0.1,0.16,.3,.8]);
nyquist(G);
a=(1-alpha)/2;
axis([0 1 -a*1.1 a*1.1])
bb=(1-alpha)/2/sqrt(alpha);
line([0 0.5],[0 0.5*bb],'linesty',':');
y2=(1-alpha)/(1+alpha)*sqrt(alpha);
line([0.5*(1+alpha) y2/bb],[0 y2],'linesty',':')
a2=axes('pos',[0.6,0.16,.35,.8]);
for i=1:3;
    alpha(i)=i*0.2;
    wm(i)=log(.1./alpha(i)/T);
    wM=log(10/T); 
    w(i,1:100)=logspace(wm(i),wM,100);
end;
for i=1:3;
    G=tf([alpha(i)*T alpha(i)],[alpha(i)*T 1]);
    bode(G,w(3,1:100));
    hold on;
end;