How to solve a matlab function on simulink? (output cannot be an mxArray in this context)

I'm using a matlab function on simulink like this:

function [u1,u2]    = fcn(To,desf,clock)
t = clock;
F=1/To;
coder.extrinsic('square');
u1=square(2*pi*F*t);
u2=square(2*pi*F*(t-desf));
end

But appears this mistake:

Function output 'u1' cannot be an mxArray in this contextoutput 'u1' cannot be an mxArray in this context. Consider preinitializing the output variable with a known type. Function 'Controlador/Controlo/Modelador/MATLAB Function1' (#248.10.12), line 1, column 11: "u1" Launch diagnostic report.

How do I solve this?

Answer 1

[Walter Roberson]

u1 = zeros(size(t));
u2 = zeros(size(t));

before doing the current assignments to u1 and u2.

[Rafael Cordero]

What if you don't know what the size of u1 and u2 will be? Is there a way around that?

[Walter Roberson]

I am not sure. You might be able to use coder.varsize