How to obtain a fixed-size array from a variable-size array

I'm using the Matlab Function block in Simulink and I have the following problem :

In my code, I have a two vectors : 'A0', of fixed-size and 'A1', of variable-size.

The size of 'A0' is 'n0', thus A0(n0,1) The maximum size of A1 is 'n0'. Thus, (Size of A1) <= (Size of A0).

One of the outputs of my Matlab Function is A = A0 + A1. Since it's a sum of vectors, they must have the same size, so what I did is fill 'A1' with zeros until reaching the same size. For exemple :

n0 = length(A0);
n1 = length(A1) ;
m = n0 - n1 ;

if n1 < n0 
    A1_1 = [A1 ; zeros(m,1)] ;
else
    A1_1 = A1 ;
end

A = A0 + A1_1 ;

I believe that with this code, 'A', 'A1_1' and 'A0' will always have the same fixed size (since the reference, 'A0', is already fixed). In my simulation, I get the value of 'A' that I desire.

The problem is that for Simulink, 'A' is still a variable-size array, so I can't branch its signal directly with some other blocks.

What I need is 'A' (or even 'A1_1') to be read by Matlab-Simulink as a fixed-size array.

Answer 1

[Ameer Hamza]

Because you are doing dynamic allocation,

A1_1 = [A1 ; zeros(m,1)] ;

MATLAB has no way of knowing what will be the final size of A1_1. To avoid such problem, try initializing A1_1 and other variables with a fixed maximum size

A1_1 = zeros(size(A0)); % or maximum size.

and then assign values to A1_1 using indexing. This way MATLAB will know in advance that what is the maximum size that these variables can take and thus consider then as fixed size array.

[David Ramsey]

That seems to fix my problem, Thank you !!

[Stephen23]

This is also explained in the MATLAB documentation:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

https://blogs.mathworks.com/loren/2012/11/29/understanding-array-preallocation/