Create MATLAB Function block with output size set at compile time

I've created a Matlab function block that takes in a parameter n from a parent mask and outputs an array of size [n,1]. I intend on using it for code generation, so the output must be fixed size.

In theory, since the mask parameters are set in the initialization script at compile time it should be possible to create a fixed size array using the parameter n.

However, when I set the output to a fixed size

and put the following code in the MATLAB function:

function y = fcn(u, n)
    % preallocate array size    
    y = zeros(n,1);
    y(:) = ones(1,n)*u
end

I receive a

"Data 'y' is inferred as a variable size matrix, while its properties in the Model Explorer specify its size as inherited or fixed. Please check the 'Variable Size' check box and specify the upper bounds in the size field."

error.

It seems that MATLAB does not recognize "n" as a parameter that won't change during the simulation. Is there any way around this?

Answer 1

[Govind KM]

Hi NJ2Cali,

It is possible that the variable n was defined as a Tunable parameter within the MATLAB Function block when it was created. This leads to Simulink interpreting the y array as variable sized because n could theoretically change during the simulation, even though it's value might not change in your case. If this is the case, To resolve this, you can set n to be non-tunable using the 'Edit Data' option from within the MATLAB Function Block.

You can refer to these answers for a little more info on this :

https://in.mathworks.com/matlabcentral/answers/79239-error-due-to-variable-size-data-in-matlab-function-block

https://in.mathworks.com/matlabcentral/answers/513980-why-are-my-matlab-function-block-arguments-being-inferred-as-variable-size?s_tid=answers_rc1-1_p1_Topic

[NJ2Cali]

This did work. Thanks!

Answer 2

[Aman]

Hi,

You can try adding the line,

u = u(1);

before

y(:) = ones(1,n)*u