Using a persistent array in a Simulink function block

I have a Simulink block that takes inputs, and remembers past inputs, in order to generate its outputs. Sometimes, the buffer to remember past inputs can be very large (20 in my case, but it could be as big as 50). I know I can use a "z" delay block to hold a past value, but I don't want to have to place 20 delay blocks on my Simulink block diagram.

Therefore, inside of my Simulink block, I am declaring this code (see below). My problem is that I get an error when running the model:

Parse error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters. Function 'DMD' (#37.187.188), line 6, column 18: "[" Launch diagnostic report.

The error above is compaining about my "States[21]" array - there are other errors as well that I did not include here.

--> How do I declare persistent arrays in my Simulink block, so that values in these arrays remain for the next time step in Simulink?

function [a11, a12, a21, a22, b1, b2] = fcn(I_in, V_out, U_in)
persistent States[21];
persistent U[21];
persistent Omega[20];

Answer 1

[Paul]

Hi richard,

The typical structure would look like this:

function [a11, a12, a21, a22, b1, b2] = fcn(I_in, V_out, U_in)
persistent States
persistent U
persistent Omega

if isempty(States)
    States = zeros(21,1); % or whatever you want to initialize as
    U      = zeros(21,1);
    Omega  = zeros(20,1)
end

% rest of code goes here

end

See Initialize Persistent Variables in MATLAB Functions for more details