If you have FRF data , invfreqs command will extract a's & b's coeffiecients & finally residue command will extract poles & residues.

[A,B] = invfreqs(frf(1:N),wi,n,n,wt,iter,tol);

[Residues,Poles,K] = residue(A,B);     % Residues & Poles, respectively

%--- Calculating the Natural Freq & Damping Ratio ---%

Damp_ratio = -real(Poles)./(abs(Poles));

% Here the natural frequency is multiplied by

% the maximum in because the frequencies were

% scaled from 0 to 1 to avoid problems in

% the invfreqs function

Nat_Frequency = abs(Poles)*max(w)/(2*pi);

This is the shortest possible code i can suggest.

Hope it helps even if it's late.