num=10;den=conv([1,1],conv([1,3],[1,5]));G=tf(num,den);
for Km=0:0.1:10000
Gc=Km;GcG=feedback(Gc*G,1);
[num,den]=tfdata(GcG,'v');
p=roots(den);pr=real(p);prm=max(pr);
pr0=find(prm>=-0.001);n=length(pr0);
if n>=1
    break
end;end
step(GcG,0:0.001:3);Km