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Logical Indexing in Simulink

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I need guidance using logical indexing in a MATLAB function block in simulink. I simply want to select rows from the A matrix based on which elements of colomn one of the matrix is greater than a certain number. For example, input_matrix = [2 1 3; 1 4 2; 4 1 6], i want to use logical indexing to select rows of input_matrix where colomn 1 element is greater or equal to 2.
In matlab this would work just fine like this:
C = input_matrix(:,1) >= 2; %logical indexing of first colomn
output_matrix = input_matrix(C,:);
And output_matrix would be [2 1 3; 4 1 6];
However i get a variable size error when i put this in a MATLAB function block in simulink.
Thanks for your help.


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Accepted Answer

Chaitanya Mallela
Chaitanya Mallela on 24 Dec 2020
Hi Femi,
The output_matrix must be declared variable size while using this logical indexing in a MATLAB function block. When you double click MATLAB function block in Simulink, it opens MATLAB editor. On this editor tab, click edit data option thats edits data properties and manages ports. For the output_matrix, check the variable size checkbox and specify an explicit size in the size column (eg: [3,3]).


Femi Bolarinwa
Femi Bolarinwa on 24 Dec 2020
The problems is that i'm dealing with a large input_matrix. Output_matrix is going to be large and i'm not going to know its size for sure. How do i get around this?
Chaitanya Mallela
Chaitanya Mallela on 24 Dec 2020
It is not necessary to specify exact dimensions, you can specify a numerical upperbound on the size to make Simulink realize a variable sized array.
Refer the documentation that demonstrates variable size declarations

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