Natural frequency/​discretiza​tion/trans​fer function/Simulink

Hi everyone!

I'm having a issue about how to get a natural frequency on a Matlab Function Block on Simulink. Here's what I got:

- g2 = ((G1*(G2+2*G_previous1+G_previous2))-(g_previous1*(2*C-2*A))-(g_previous2*(C+A-B)))/(A+B+C);

where g2 is a discretized signal based on a second order transfer function (G/ (s^2 + 2ksi wn + 2 wn^2))

where:

A = 4/(T^2);

B = (4*ksi*wn)/T;

C = (wn)^2;

my point is: I fixed the values of wn and ksi, but how can a give a step or damp to get the natural frequency of the system, since the g2, G2 and the previous ones are getting updated when I run my model?

[VBBV]

Use damp function to get the natural frequency and damping ratio

%if true
  % code
% end
[wn zeta] = damp(sys)

Where sys is the discrete time transfer function of your model obtained using tf

[Gustavo Araujo]

But can I call on tf the constants or do I need to put values?