Problem to get m-code work with user-defined functions (e.g. persisent)

Hello,

i'm really new to matlab and wrote some m script code and now i want to use this code in a model that i created with simulink - simscape. I found out thats possible to use the user-defined functions to solve that problem. I'm using the MATLAB Function Block to execute my code but i'm struggeling in initalizing a persistent variable. Here is a snipped out of my code:

   function [O_y_m, O_Net_Weights, O_Stepsize_Weights] = rbf_net(input_flag,u_old,y,y_old)
  %#codegen 
   persistent NET_CENTERS;
   NET_INPUT = 3;
   NET_HIDDEN = 6;
   if(input_flag == 0) %also tried if(isempty(NET_CENTERS))
      NET_CENTERS     = randn(NET_HIDDEN,NET_INPUT);
   end   
   X = [u_old, y, y_old];
   H = zeros(NET_HIDDEN,1); 
   for j = 1:NET_HIDDEN
       ekl_dist = norm (X-NET_CENTERS(j));
       H(j) = exp(-(ekl_dist)/(2 * B(j)^2));
   end

I get the following error:

   Persistent variable 'NET_CENTERS' is undefined on some execution paths.

Matlab provides this to initalize a persistent variable

   function findProduct(inputvalue) %#codegen
   persistent PROD_X

   if isempty(PROD_X)
      PROD_X = 1;
   end
   PROD_X = PROD_X * inputvalue;
   end

Already tried this before. It only works in the m-code.

Maybe this is the wrong way of using it but i try to explain what i want to do: I need something like a global variable for my function that must be a matrix and should only initialized at sample time 0. The Dimension will be determined by two constants that i will change from time to time (not in the code, only a manual way after i evaluated the results of my model). This matrix must be updated in the function and it values must be also there, when the function will be executed at the next sample time.

Thanks for your further help!

with kind regards

[Jan]

The important detail is:

 It only works in the m-code

Please explain this.

[Tobias Orth]

I created a Matlab-Script file *.m an coded there my program. There i can execute the program without any problems. So no errors and no warnings

Answer 1

[Image Analyst]

I don't know Simscape but it thinks that this line

if(input_flag == 0)
    NET_CENTERS     = randn(NET_HIDDEN,NET_INPUT);
end

may not get executed if you never pass in a flag of 0. And later on you go on to use NET_CENTERS in a for loop which definitely will get executed. Well, if NET_CENTERS never got assigned, then the line in the for loop will bomb. That's what it's warning you about. And I think it's probably a warning rather than an error. You can either ignore it, or (better and more robust) initialize it after checking if it's empty by using isempty(), like your MATLAB example function did.

% Add this if block to initialize in case NET_CENTERS has not been assigned yet.
if isempty(NET_CENTERS)
      NET_CENTERS = randn(NET_HIDDEN,NET_INPUT);
end

[Tobias Orth]

Thanks for your answer.

This was only anther try because it doesn't work with the isempty(). And it's a error, which occurs when i try to run the model. So i can't ignore this. User-defined Functions can be found under Simulink - User-Defined Functions. It's nothing related to simscape.

Answer 2

[Tobias Orth]

solved the problem. i created a new model with only the matlab function block and transfered it line by line to determine the error, but i works like magic... Have now the code 1:1 in the new model, which is working. I also want to have a matrix as a return parameter, which only works when you define fixed size matrix. So a defined in the model explorer under my matlab function the net_hidden as a parameter and added it also to workspace where i defined the size. So if i want to change the size of the matrix i have to change the parameter in the workspace