function Gc=ralag1(G,s1,kc)
G=tf(G);[r,k]=rlocus(G);
ng=G.num{1};dg=G.den{1};ngv=polyval(ng,s1);dgv=polyval(dg,s1);g=ngv/dgv;
theta_G=angle(g);theta_s=angle(s1);MG=abs(g);Ms=abs(s1);
Tz=(sin(theta_s)-kc*MG*sin(theta_G-theta_s))/(kc*MG*Ms*sin(theta_G));
Tp=-(kc*MG*sin(theta_s)+sin(theta_G+theta_s))/(Ms*sin(theta_G));
Gc=tf([Tz 1],[Tp 1])