Taking error message in matlab

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 

[Torsten]

Is something unclear about what the error message means ?

A_lat has 5 rows, B_lat has 4 rows. But both must have the same number of rows.

[Ahmet Akcura]

But in our book, it is like in that format. What should we do? Also when I add one row to the B, now it says A and C must have the same number of row???

[Torsten]

Take away one row in A :-)

In the documentation of ss, the sizes of the input matrices to be compatible are listed:

https://de.mathworks.com/help/control/ref/ss.html

[Edward Tomanek]

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?

Answer 1

[Edward Tomanek]

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]

Thank you so much but I need to use these matrix. Do you know how can use ss fuction for this code in other way?

[Steven Lord]

If A has 5 rows and B has 4 rows, the values A*x and B*u must have 5 and 4 rows respectively. Adding together matrices with different numbers of rows is not mathematically defined. I would double check that I'd copied the A_lat, B_lat, etc. matrices correctly from whatever paper / book / etc. I was trying to implement.

[Ahmet Akcura]

Thank you so much for your effort, I found my mistake :)