G=tf(1,[conv([1 4],[1 4 20]),0]);
hold off; rlocus(G);  axis('square')
[K,P]=rlocfind(G)

[R,K]=rlocus(G); 
for i=1:length(K)-1
   K1(3*i-1)=K(i); 
   K1(3*i-2)=K(i)+(K(i+1)-K(i))/3;
   K1(3*i)=K(i)+2*(K(i+1)-K(i))/3;
end
R=rlocus(G,K1); plot(R'), axis('square')
[xx,yy]=rlasymp(G); hold on; plot(xx,yy,':')