Error using ss. How do i fix this?

My current code is below. This is my error code:

Error using ss (line 345)
The values of the "a" and "b" properties must be matrices with the same number of rows.

Error in Project43 (line 33)
sys=ss(A,BS,Chead,D);

>>

I have tried everything I know how to do to fix it, but it is not working. Any suggestions?

m1=5.3;
m2=28.5;
m3=8.6;
m4=12.8;
c1=400;
c2=4750;
c3=4585;
c4=4475;
k1=310000;
k2=183000;
k3=162800;
k4=90000;


t=0:0.01:5;
A=[0 0 0 0 1 0 0 0; 0 0 0 0 0 1 0 0; 0 0 0 0 0 0 1 0; 0 0 0 0 0 0 0 1; -k1/m2 k1/m2 0 0 -c1/m2 c1/m2 0 0; k1/m2 -k1/m2 k2/m2 0 c1/m2 (-(c1/m2)-(c2/m2)) c2/m2 0; 0 k2/m3 (-(k2/m3)-(k3/m3)) k3/m3 0 c2/m3 (-(c2/m3)-(c3/m3)) c3/m3; 0 0 k3/m4 (-(k3/m3)-k4/m4) 0 0 c3/m4 (-(c3/m4)-(c4/m4))];
D=[0];

EV=eig(A);

dt=0.01;
tf=5;
t=0:dt:tf;


%for head displacement x1
Chead=[1 0 0 0 0 0 0 0]; 

%For Us 
BS=[0 0 0 0 0 0 k4/m4 0]; 
sys=ss(A,BS,Chead,D); 
[yS,t,x]= step(sys,t) ; 
%For UI 
BI=[0 0 0 0 0 0 0 c4/m4 ]; 
sys=ss(A,B,Chead,D); 
[yI,t,x]= impulse(sys,t) ; 
Yhead=yS+yI; 
plot(t,Yhead) 


% For torso displacement
Ctorso=[ 0 1 0 0 0 0 0 0];
%For Us 
BS=[0 0 0 0 0 0 k4/m4 0]; 
sys=ss(A,BS,ctorso,D); 
[yS,t,x]= step(sys,t) ; 
%For UI 
BI=[0 0 0 0 0 0 0 c4/m4 ]; 
sys=ss(A,BS,Ctorso,D); 
[yI,t,x]= impulse(sys,t); 
Yhead=yS+yI; 
plot(t,Ytorso-Yhead)


%Repeat for head acceleration x1double dot using Cheadacc=[-k1/m1 k1/m1 0 0 –c1/m1 c1/m1 0 0] and plot(t,x1doubledot/9.81) 



Cheadacc=[-k1/m1 k1/m1 0 0 -c1/m1 c1/m1 0 0];
%For Us 
BS=[0 0 0 0 0 0 k4/m4 0]; 
sys=ss(A,BS,Cheadacc,D); 
[yS,t,x]= step(sys,t); 
%For UI 
BI=[0 0 0 0 0 0 0 c4/m4 ]; 
sys=ss(A,BS,Cheadacc,D); 
[yI,t,x]= impulse(sys,t) ; 
Yhead=yS+yI; 
plot(t,x1doubledot/9.81)

Answer 1

[Star Strider]

Transpose ‘BS’ to a column vector (everywhere you use it, since you re-define it):

BS=[0 0 0 0 0 0 k4/m4 0].'; 

Do the same for ‘BI’.

There are a number of other problems and undefined variables. You need to solve those problems, since what you are doing is not obvious.

[Anna Zito]

Thank you!!

I fixed that as well as the undefined variables. Only one figure is showing up. How do i get all three plots to show up?

[Star Strider]

My pleasure!

The plots will replace the previous plots unless you create each one in a new figure. So, before each plot call, open a new figure.

Example —

figure
plot(t,Yhead) 

and so for the rest. You can also experiment with the subplot function with them.

[Star Strider]

If my Answer helped you solve your problem, please Accept it!

.