lsim function not work for polynomial model

a= lsim(sys_MIMO(1, 1),X_filt(:,1),t_new) %based on transfer function model works

b= lsim(sys_MIMO1(1, 1),X_filt(:,1),t_new) %based on polynomial model error popup

%Error using DynamicSystem/lsim (line 84)

%For models with unspecified sample time, time is counted in samples and the time increment must be 1 (one %sample).

Answer 1

[Paul]

I'm not sure what a "polynomial model" is. But that error message means that lsim is being called on a discrete time system that has an unspcifiied sample time, but the time vector input to lsim is not [0 1 2 3 4 5 ....] (actually, the first point doesn't have to be 0 I don't believe).

For example define a discrete time system with sample time = 0.1 and simuate it for 1 second

sys = tf(1,[1 .5],0.1);
t = 0:.1:1;
y = lsim(sys,sin(t),t); % works

Now define a discrete time system with undefined sample time an simulate it for 11 samples

sys = tf(1,[1 .5],-1)

sys =
 
     1
  -------
  z + 0.5
 
Sample time: unspecified
Discrete-time transfer function.

n = 0:10;
y = lsim(sys,sin(n),n); % works

But an error results with

y = lsim(sys,sin(t),t)

Error using DynamicSystem/lsim (line 84)
For models with unspecified sample time, time is counted in samples and the time increment must be 1 (one sample).

So sys_MIMO1 either needs to have a sample time defined, or you'll have to lsim() it with a sequence of integers as the time input.

[zhenzhen Jiang]

thanks, it works