# Could not determine the size of this expression

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Joseph on 9 May 2024
Answered: Hassaan on 9 May 2024
n_y = 2; Np = 7;
%% Output sequences
Yref=zeros(n_y*Np,1);
%Yref(1:2,1)=[Rr*real(Vo_xy_ref),Rr*imag(Vo_xy_ref)] ; % Construct output reference sequence
Yref(1:2,1)=Rr*Vo_xy_ref;
for k=n_y+1:n_y:n_y*Np
row_i=k;
row_f=k+n_y-1;
Yref(row_i:row_f,:)=Rr*Yref(row_i-n_y:row_f-n_y,:);
end
Error:Could not determine the size of this expression.
Function 'Model Predictive Control 1' (#39.4046.4065), line 157, column 33:
"row_i-n_y:row_f-n_y"
This portion of code works on its own as a .m file in matlab but when placed in a simulink model (matlab function block) gives this error any suggestions?

Hassaan on 9 May 2024
Try this:
function Yref = generateYref(n_y, Np, Rr, Vo_xy_ref)
% Define the size of the output explicitly
Yref = zeros(n_y * Np, 1);
% Make sure Vo_xy_ref is defined or passed as a parameter
% Assuming Rr is scalar and Vo_xy_ref is complex number or 2-element vector
if isreal(Vo_xy_ref)
Yref(1:2) = Rr * [real(Vo_xy_ref); imag(Vo_xy_ref)];
else
Yref(1:2) = Rr * Vo_xy_ref; % Adjust this based on the actual type of Vo_xy_ref
end
% Loop to propagate the values
for k = n_y + 1 : n_y : n_y * Np
row_i = k;
row_f = k + n_y - 1;
% Safeguard for bounds
if row_f <= n_y * Np
Yref(row_i:row_f) = Rr * Yref(row_i - n_y : row_f - n_y);
end
end
end
Suggestions for Debugging in Simulink:
• Check Data Types and Sizes: Use the Model Explorer or other Simulink diagnostic tools to check data types and sizes. Make sure they are what you expect.
• Simulink Configuration Parameters: Check your Simulink model configuration parameters for settings that might affect matrix operations, such as algebra simplifications and data type inheritance.
• Simulink Diagnostic Viewer: When you run the simulation, Simulink provides detailed error messages and warnings in the Diagnostic Viewer, which can offer more insights into what might be causing the problem.
If you continue to encounter issues, consider breaking down the function into smaller parts to isolate which part specifically causes the error in Simulink. Additionally, review Simulink documentation on how to handle matrix operations and array indexing within MATLAB Function blocks, as there are often specific constraints and best practices to follow.
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