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# Error file output dimensions

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Dhruv Thakkar on 24 Feb 2020
Commented: Dhruv Thakkar on 5 Apr 2020
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.
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Dhruv Thakkar on 5 Apr 2020
I used the signal dimension block to make sure everything is consistent.

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### Accepted Answer

Jyotsna Talluri on 27 Feb 2020
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
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R2018b

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