function [Gc,KK]=rlag(G,zeta,ew,Tz);
if nargin<4,Tz=0.1;end;if nargin<3,ew=5;end;if nargin<2,zeta=0.707;end;
G=tf(G);[r,k]=rlocus(G);
za=zeta/sqrt(1-zeta^2);ri=r(1,find(imag(r(1,:))>0));
ra=imag(ri)./real(ri);KK=spline(ra,k(find(imag(r(1,:))>0)),1/za);
syms x Gn Gd;Gn=poly2sym(G.num{1});Gd=poly2sym(G.den{1});ess=limit(Gn*KK/Gd*x);
beta=round(100/sym2poly(ess)/ew);Tp=Tz/beta;Gc=tf([1 Tz],[1 Tp]);
Gcl=feedback(G*Gc*KK,1);step(Gcl);hold on;step(feedback(G,1));