# Taking error message in matlab

3 views (last 30 days)
Ahmet Akcura on 21 Jun 2022
Commented: Ahmet Akcura on 21 Jun 2022
In the below, we have our matlab code but we are taking error and error massage is;
Error using ss (line 355)
The "A" and "B" matrices must have the same number of rows.
Error in lateral (line 34)
MSS = ss(A_lat,B_lat,C_lat,D_lat)
What should we do? If you have any suggestion for us, we will be very happy.
The code is ;
%parameters
Mach = 0.206;
U_zero = 70;
q_dot = 2997;
alpha_zero = 11.7;
gamma_zero = 0;
g = 9.81;
%lateral values
Y_b = -21.1;
L_dotb = -10.4;
L_dotp = -1.43;
L_dotr = 0.929;
N_dotb = 1.44;
N_dotp = -0.026;
N_dotr = -0.215;
Y_starsa = -0.004;
Y_starsr = 0.0053;
L_dotsa = 2.74;
L_dotsr = 0.7;
N_dotsa = 0.42;
N_dotsr = -0.67;
A_lat = [Y_b 0 -1 g/U_zero 0; L_dotb L_dotp L_dotr 0 0; N_dotb N_dotp N_dotr 0 0; 0 1 0 0 0; 0 0 1 0 0];
B_lat = [0 Y_starsr; L_dotsa L_dotsr; N_dotsa N_dotsr ; 0 0];
C_lat = [1 0 0 0; 0 1 0 0; 0 0 1 0; 0 0 0 1];
D_lat = [0; 0; 0; 0];
I = eye(4,4);
figure(3)
MSS = ss(A_lat,B_lat,C_lat,D_lat)
Transfer=tf(MSS)
step(MSS,3000)
grid on
Edward Tomanek on 21 Jun 2022
I know what you mean, but all MATLAB is telling you is that all those matrices need to have the same number of rows for the function to work. I don't know the specifics of the example at hand but if matrix A_lat ends up having more rows there may be some way to convert it to having a lower number of rows?

Edward Tomanek on 21 Jun 2022
Hi,
In the line:
MSS = ss(A_lat,B_lat,C_lat,D_lat)
You are using the state-space model, documentation found here https://uk.mathworks.com/help/control/ref/ss.html
Your error message is telling you that all the matrices need to have the same number of rows for this function to work. For example, using
A = [1, 2; 3, 4; 5, 6]
B = [2, 3; 4, 5]
would not work because A has 3 rows and B only has 2 (i.e. all the matrices need to have the same numbers of semi-colons).
Notice that in your definitions, B_lat, C_lat and D_lat all have 4 rows but A_lat has 5. That is what's causing the error.
Regards,
Edward
Ahmet Akcura on 21 Jun 2022
Thank you so much for your effort, I found my mistake :)

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