How to define an array based on Simulink simulation time?

Hello everyone, I'm attempting to define an array in a MATLAB Function block based on the simulation time in Simulink. In my code, I use 'times index' to record the number of simulation steps. I have set the time step to 0.01s.To achieve this goal, I used 'persistent' variables, but encountered an error. How can I implement my objective?

function [y,y1] = fcn(u)
persistent inputs;  % 声明一个持久变量用于保存输入值
persistent time_index; 
if isempty(inputs)  % 如果持久变量为空，则初始化
    inputs = u;     % 将当前输入值保存到持久变量中
    time_index = 1;
else
    inputs = [inputs, u];  % 将当前输入值追加到持久变量中
    time_index = time_index + 1;
end
% 计算平均值
mean_val = mean(inputs);
% 计算差值的平方
diff_squared = (inputs - mean_val).^2;
% 计算方差
y = sum(diff_squared) / length(inputs);
all_inputs(time_index) = u;
y1=all_inputs;

This is the error I encountered.

Answer 1

[Rishav]

Hi guo,

I understand that you are trying to initialize an array based on Simulink simulation time but encountering the 'Undefined function or variable "all_inputs"' error.

The issue here is that you are trying to use 'all_inputs' without declaring it as a 'persistent' variable, which would cause errors.

Just add the following line in your code:

persistent all_inputs;

[guo qing]

Hello, thank you for your response. I wanted to ask why it is necessary to name it as a persistent variable. Are there any other ways to initialize an array based on time in Simulink?"

[guo qing]

I tried the operation you suggested, but MATLAB requires me to initialize all_inputs using the if isempty command and it cannot be an empty array. Clearly, the size of the all_inputs array will change over time, for example, with changes in simulation time. Is there a good way to solve this problem, or do I have to