Why I get a 3 dimensional array using to workspace block?

Hello everybody. I have a for loop which its output is 2 by N. N can be 1000 for example. And I define this for loop inside matlab function block in simulink. When I want to get output from it, it is defined as 2 by 1000 by 51. I mean it becomes 3 Dimensional! Why this happens and how to solve it? I also saw this problem when I wanted to integrate a matlab function. I need the output be M by N, but not M by N by D.

[Torsten]

Why this happens and how to solve it?

You gave us too little information to be able to answer this.

[Faezeh Yousefpour]

This is my main code which I used in matlab function block. The output is Yt

dt = 0.005; %sample time
t = 0:0.01:2;
N = length(t);
Q1 = 9e-4;
Q5 = 1e-5;
R1 = 0.1;
R2 = 0.01;
Q = diag([Q1, Q5]);
Q6 = diag([Q1, 0,0,0,Q5]);
R = diag([R1, R2]);
ms = 1242;
mu = 100;
k1s = 80000;
k2s = 32000;
c1s = 4000;
c2s = 1600;
kt = 405000;
ms = 1242;
mu = 100;
k1s = 80000;
k2s = 32000;
c1s = 4000;
c2s = 1600;
deltacs = 775;
csbar = 2800;
kt = 405000;
g = 9.81;

xt = zeros(5,N);
yt = zeros(2,N);
for i = 1:N-1
    
    xt(:,i+1) = xt(:,i) + 0.005*(PASSIVEF(xt(:,i)));
    
    
    yt(:,i+1) = (MeasurementMatrix(xt(:,i))) ;
end
Yt = yt;
%%

And these are functions defined inside the code

function y = MeasurementMatrix(x)
ms = 1242;
mu = 100;
k1s = 80000;
k2s = 32000;
k2 = 32000;
c1s = 4000;
c2s = 1600;
deltacs = 775;
csbar = 2800;
kt = 405000;
Fa = 2100;
V = 20;
ds0 = -0.1590;
dt0 = -0.0325;
g = 9.81;
x1 = x(1);
x2 = x(2);
x3 = x(3);
x4 = x(4);
x5 = x(5);
cs = deltacs*atan(1000*(x(4)-x(3)) +csbar);
y1 =( kt*x1+k1s*(x5-x2) + k2s*(x5-x2)^3 -k1s*x5-k2s*x5^3 +cs*(x4-x3))/mu;
y2 = g*(-k1s*(x5-x2) -k2s*(x5-x2)^3 +k1s*x5+k2s*x5^3 ...
    -cs*(x4-x3))/(-k1s*x5-k2s*x5^3);
y = [y1;y2];
end
%% 
function x = PASSIVEF(x)
dt = 0.005;
Q1 = 9e-4;
Q5 = 1e-8;
R1 = 0.1;
R2 = 0.01;
Q = diag([1 1 1 1 1]);
R = diag([R1, R2]);
Qn = [Q1 0; 0 Q5];
ms = 1242;
mu = 100;
k1s = 80000;
k2s = 32000;
c1s = 4000;
c2s = 1600;
kt = 405000;
ms = 1242;
mu = 100;
k1s = 80000;
k2s = 32000;
c1s = 4000;
c2s = 1600;
deltacs = 775;
csbar = 2800;
kt = 405000;
Fa = 2100;
Vlc = 20;
ds0 = -0.1590;
dt0 = -0.0325;
g = 9.81;
x1 = x(1); x2 = x(2); x3 = x(3); x4 = x(4); x5 = x(5);
cs = deltacs*atan(1000*(x4-x3)) +csbar;
numerator1 = kt*x1 + k1s*(-0.15 - x2) +k2s*(-0.15-x2)^3 +ms*g ;
numerator2 =cs*(x4-x3);
x =[-x3;
    x3 - x4;
    (numerator1+numerator2)/mu;
    ((-k1s*(-0.15-x2) - k2s*(-0.15-x2)^3 +ms*g -cs*(x4-x3)))/ms;
    0] ;
x = x +dt*x;
end

[Torsten]

Can you think of a reason for the number 51 as the third dimension ? Maybe some variable that is set to have 51 elements ?

What is input to the function block ?

[Faezeh Yousefpour]

I didn't define any input to the function. Once I put clock block and to workspace block, time length was 1 by 51! I used 2D array in to workspace block, still I got 3D array! It is related to time! I even defined t as input to the function, again I received 3D array!

Answer 1

[Shivam Gothi]

Hello @Faezeh Yousefpour,

As per my understanding, you are trying to log the 2d array which is an output from MATLAB function block. But instead of being a 2D array, it is a 3D array.

Here, the third dimension is corresponding to the “time step”. That is, the 2D array may have different values at different simulation time-steps. Therefore, Simulink exports the value of 2D array at every time-step, thus making it a 3D array. For an example, suppose that the MATLAB function outputs a (2 x 3) array and simulation takes 5 time steps, then your logged data will be (2 x 3 x 5). As depicted in below figure. In your case, it is (2 x 1000 x 51), because the simulation takes 51 steps.

You cannot get rid of it. But, as a work-around, you can extract the 2D array at time step (N), from the 3D array by typing the below command in MATLAB command window.

Two_D_Array = simout(:,:,N); 
% This will extract the 2D matrix at Nth time step, which is the output of
% MATLAB function.

The below given figure shows the worksace variables. We can see that the variable "Two_D_Array" is extracted and has dimention (2 x 1000)

(Note: here, the data is exported as “Array” (look inside the “save format” field found in “block parameters” of “simout” block)

I have attached the demo Simulink model containing a “MATLAB function” block, which outputs a (2 x 1000) matrix.

I hope this helps !