I don't understand where the problem is in this system

if true
  % code
switch es
case 1, beta=0.1;  k=2;  x0=[0;0];   w0=0; tmax=20;
case 2, beta=0.01; k=2;  x0=[0;0];   w0=0; tmax=200;
case 3, beta=10;   k=20; x0=[0;0];   w0=0; tmax=10;
case 4, beta=0.1;  k=2;  x0=[0;0.2]; w0=0; tmax=20;
case 5, beta=0.1;  k=2;  x0=[0;0];   w0=4; tmax=10;
case 6, beta=0.01; k=2;  x0=[0;0];   w0=4; tmax=10;
case 7, beta=10;   k=20; x0=[0;0];   w0=4; tmax=10;
case 8, beta=0.1;  k=2;  x0=[0;0.2]; w0=4; tmax=10;
end
m=0.2;
f0=1;
A=[0,-k/m; 1,-k/beta];
B=[1/m,0;0,0];
C=[1,0];
D=0;
sistema=ss(A,B,C,D);
T=0:0.01:tmax;
U=f0*cos(w0*T);
[y,tsim,x]=lsim(sistema,U,T,x0);
end

The error is: Error using DynamicSystem/lsim (line 84) When simulating the response to a specific input signal, the input data U must be a matrix with as many rows as samples in the time vector T, and as many columns as input channels.

Thanks to all!

Answer 1

[Jan]

The message seems to be clear:

 U must be a matrix with as many rows as samples in the time vector T, 
 and as many columns as input channels.

We cannot run your code, e.g. because "k" is undefined. But is looks like U and T have the same number of elements. Then it might be the number of input channels. Did you test this already?

[marco mezzolla]

Thanks for the answer! "k" is defined in the switch. I'm trying to learn on my own, and I don't understand how many input channels I have in the code.

[Jan]

Sorry, I've overseen "k". A search in the net or in this forum is always a good idea. See e.g.:

• https://de.mathworks.com/matlabcentral/answers/76274-error-in-my-code

Does D=0 mean, that the system has no input and output channels? I'm not familiar with Simulink, therefore I assume others might post more useful answers.