MATLAB: 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 problem

lsim

clear all clc
Ms = 267; Mu = 36.6; Ks = 18.742; Kt = 193.915; Bs = 700; Bt = 200;
A = [0 1 0 0; -Ks/Ms -Bs/Ms Ks/Ms Bs/Ms; 0 0 0 1; Ks/Mu Bs/Mu -(Kt+Ks)/Mu -(Bt+Bs)/Mu]; B = [0 0;0 0;0 0; Kt/Mu Bt/Mu]; C = [1 0 0 0 ; 0 0 1 0]; D = [0];
t = 0:0.01:10; u = 100*sin(5*t); sys = ss(A,B,C,D); x0 = [0;0;0;0];
y = lsim(sys,u,t,x0) x1 = y(:,1); x2 = y(:,1);

Best Answer

Since ‘B’ has two columns, ‘u’ must have two rows:
This works:
Ms = 267; Mu = 36.6; 
Ks = 18.742; Kt = 193.915;
Bs = 700; Bt = 200;
A = [0 1 0 0; -Ks/Ms -Bs/Ms Ks/Ms Bs/Ms; 0 0 0 1; Ks/Mu Bs/Mu -(Kt+Ks)/Mu -(Bt+Bs)/Mu];
B = [0 0;0 0;0 0; Kt/Mu Bt/Mu];
C = [1 0 0 0 ; 0 0 1 0];
D = [0]; 
t = 0:0.01:10;
u = 100*sin(5*t);
u = repmat(u, 2, 1);
sys = ss(A,B,C,D);
x0 = [0;0;0;0];
y = lsim(sys,u,t,x0);
x1 = y(:,1);
x2 = y(:,2);
figure(1)
plot(t, x1,  t, x2)
grid
You also referenced solumn 1 in both ‘x1’ and ‘x2’. I corrected that, and added the plot call.
Related Question