The following function finds the values of K L T from the transfer function. I need to find these values from a STEP response which is like an input to the mat file. Here G is the Transfer Function in the file.
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function [K,L,T]=getfod(G,method)
K=dcgain(G);
if nargin==1
[Kc,Pm,wc,wcp]=margin(G); ikey=0; L=1.6*pi/(3*wc); T=0.5*Kc*K*L;
if isfinite(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
elseif nargin==2 & method==1
[n1,d1]=tfderv(G.num{1},G.den{1}); [n2,d2]=tfderv(n1,d1);
K1=dcgain(n1,d1); K2=dcgain(n2,d2);
Tar=-K1/K; T=sqrt(K2/K-Tar^2); L=Tar-T;
end
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];
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