Error file output dimensions

I am trying to create an Adaptive Model Predictive control to hold a pendulum at a certain angle (theta), assuming a rotory actuator at the pivot of the pendulum and the mass being connected using a rigid massless rod. I wrote the following file to give the plant dynamics

function y   = fcn(u,T)
%% u(1) : Angular Position (rad) u(2) : Angular rate (rad/s)
%T is the applied torque(N/m)
y = zeros([2 1]);
y(1) = u(2);    % Angular rate
y(2) = 9.81/0.5*sin(u(1))-T/3/0.5; %Angular Acceleration 

Hence the output of the file should be a [2 x 1] matrix, but when I ran the following command

>> set_param(bdroot,'ShowLineDimensions','on')

It showed the line dimension as 2(scalar). What is going wrong here? I fail to understand.

I have attached the Simulink file along with the question.

[Walter Roberson]

I suspect that Simulink drops all trailing 1 in the shape.

[Dhruv Thakkar]

Then why does it show this error.

Error in port widths or dimensions. The signal connected to the "Model.DX" port of the "untitled/Adaptive MPC Controller" block must be a matrix signal of 2 rows and 1 columns.

Component:Simulink | Category:Model error

Error in port widths or dimensions. Output port 1 of 'untitled/Adaptive MPC Controller/MPC/MPC Matrix Signal Check DX/Input' is a one dimensional vector with 2 elements.

Component:Simulink | Category:Model error

[weiwei cao]

I met the same error, so how did you get rid of it?

Thanks a lot~

[Dhruv Thakkar]

I used the signal dimension block to make sure everything is consistent.

Answer 1

[Jyotsna Talluri]

The output of the MATLAB function block is by default not set to variable size unless we enable the Variable size check box in the MATLAB Function block editor, in the Edit data of the MATLAB Function block editor, you can specify the output signal size to be [2 1]. But this output is the input to the integrator in the Plant Model subsystem of your model which does not support variable size input. So, use reshape block to convert vector of data to a matrix of required dimensions [2 1], when inputting the output signal from Plant Model to Update Model

Refer to the below link

https://la.mathworks.com/help/simulink/slref/reshape.html