function [K,L,T,G1]=getfolpd(key,G)
switch key
    case 1,[y,t]=step(G);
        fun=inline('x(1)*(1-exp(-(t-x(2))/x(3))).*(t>x(2))','x','t');
        x=lsqcurvefit(fun,[1 1 1],t,y);K=x(1);L=x(2);T=x(3);
    case 2,[Kc,Pm,wc,wcp]=margin(G);
        ikey=0;L=1.6*pi/(3*wc);K=dcgain(G);T=0.5*Kc*K*L;
        if finite(Kc),x0=[L;T];
            while ikey==0,u=wc*x0(1);v=wc*x0(2);
                FF=[K*Kc*(cos(u)-v*sin(u))+1+v^2;sin(u)+v*cos(u)];
                J=[-K*Kc*wc*sin(u)-K*Kc*wc*v*cos(u),-K*Kc*wc*sin(u)+2*wc*v;wc*cos(u)-wc*v*sin(u),wc*cos(u)];x1=x0-inv(J)*FF;
                if norm(x1-x0)<1e-8,ikey=1;else,x0=x1;end,end
            L=x0(1);T=x0(2);end
    case 3,[n1,d1]=tfderv(G.num{1},G.den{1});
        [n2,d2]=tfderv(n1,d1);K1=dcgain(n1,d1);
        K2=dcgain(n2,d2);K=dcgain(G);Tar=-K1/K;
        T=sqrt(K2/K-Tar^2);L=Tar-T;
    case 4
        Gr=opt_app(G,0,1,1); L=Gr.ioDelay;
        T=Gr.den{1}(2)/Gr.den{1}(2);K=Gr.num{1}(end)/Gr.den{1}(2);
end
G1=tf(K,[T 1],'ioDelay',L);
function [e,f]=tfderv(b,a)
f=conv(a,a);na=length(a);nb=length(b);
e1=conv((nb-1:-1:1).*b(1:end-1),a);
e2=conv((na-1:-1:1).*a(1:end-1),b);
maxL=max(length(e1),length(e2));
e=[zeros(1,maxL-length(e1)) e1]-[zeros(1,maxL-length(e2)) e2];