How to assign values to a matrix with a for loop when using PLC Coder?

Hello, I have a simulink model containing a user defined Matlab function that I want to generate PLC code from. Within that function I am assigning some values to a matrix uising a for loop.

Mini Code Example:

function y = fcn()
U = zeros(30, 30);
for i=1:2
    U(i:30, i) = ones(31-i,i);
end
y = U;

When I check the subsystems compatibility for PLC Code Generation in simulink I get the following error:

"Variable-size arrays are currently disabled for code generation. Consider selecting the 'Support variable-size signals' option on the Configuration Parameters > Code Generation > Interface page."

Does anybody know how to solve this?

(When I write the assignment line by line by hand, it works perfectly fine. But in practice I have a lot more than 2 assignments. Thats why I want to use a for loop)

Thanks for any advice!!!