Blocks updates persistent or state variables while computing outputs

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Matteo Paiano
Matteo Paiano on 20 Sep 2021
Commented: Sargondjani on 20 Sep 2021
In Simulink I had a MATLAB function working properly. I change it a little bit, but now I get the error:
"'DynProg/referenceS/Willners' or the model referenced by it contains blocks that updates persistent or state variables while computing outputs and is not supported in an algebraic loop. The parent subsystem 'DynProg/referenceS' is in an algebraic loop with the following blocks"
function [u_opt,r_des] = optimal_heading(current_X_ASV,X_AUV_list,P_AUV_list,u_max,r_max,Tc_usbl,decisions)
X = current_X_ASV'; Cost = 0; action = [-1 -1]; LA = -1;
coder.varsize('expansion',[10000 7], [1 0])
expansion = [X,Cost,action,LA];
psi_set = (2*r_max*Tc_usbl).*rand(1,decisions) - r_max*Tc_usbl;
u_set = u_max.*rand(1,decisions);
delta_opt = action(1); u_opt = action(2);
r_des = delta_opt/Tc_usbl;
The code is much longer than this, but I tried commenting and uncommenting some lines and I came to the conclusion that the use of rand is somehow responsible for the error. However, if I create a simple function like
function fcn(r_max, Tc_usbl, decisions)
psi_set = (2*r_max*Tc_usbl).*rand(1,decisions) - r_max*Tc_usbl;
for k = 1:numel(psi_set)
delta = psi_set(k)
end
It works fine! The previous version of the function used a simple linspace, and if I still use it instead of rand, the code compile correctly.
Do you have any suggestion! Thanks, really!
  1 Comment
Sargondjani
Sargondjani on 20 Sep 2021
what are the state variables? I mean, the error suggests that you change your state variables in the function optimal_heading

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