function K0=ps14e_6242_2004(n)
% function K0=ps14e_6242_2004(n)
%
% gain margin estimation for Problem 1.4(e) in 6.242/2004
[g,rGns]=ps14d_6242_2004(n);
rGn=((n-1)/n)*ps14a_6242_2004(n);           % reduced model
K1=1;                                       % some feedback gain
GK1=K1/(1+K1*rGn);                          % closed loop
[z,p,k]=zpkdata(GK1);                       % closed loop poles
sm=max(real(p{1}));  
fprintf('\nStability margin:  %f',sm);
sg=norm(GK1,Inf)*g;
fprintf('\nSmall gain margin: %f',sg);
if (sm<0)&(sg<1),                           % stability check
    fprintf('\nNominal stabilty established');
    rGns=rGns(abs(imag(rGns))<=g);
    y=min(real(rGns)-sqrt(g^2-imag(rGns).^2));
    K0=-1/y;
else
    fprintf('\nNominal stabilty not established');
end