Reinforcement Learning - How to use a 'trained policy' as a 'controller' block in SIMULINK

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I am folowing the example "Train DDPG Agent to Swing Up and Balance Cart-Pole System" shown here. I am trying to use the 'trained' policy as a controller in SIMULINK for the Cartpole Pendulum system but I am having issues. I used the "generatePolicyFunction" function in Matlab to create the evaluatePolicy.m file, which contains the policy function, and the agentData.mat file, which contains the trained deep neural network actor. I am a bit confused on how to use the generated policy function in SIMULINK to replace the RL Agent block and have it as the controller (policy) for the plant. Below is a screenshot of my Simulink model.
Here is the main code following the Matlab example mentioned above:
mdl = 'rlCartPoleSimscapeModel';
env = rlPredefinedEnv('CartPoleSimscapeModel-Continuous');
actInfo = getActionInfo(env);
obsInfo = getObservationInfo(env);
numObservations = obsInfo.Dimension(1);
Ts = 0.02;
Tf = 25;
statePath = [
imageInputLayer([numObservations 1 1],'Normalization','none','Name','observation')
actionPath = [
imageInputLayer([1 1 1],'Normalization','none','Name','action')
commonPath = [
criticNetwork = layerGraph(statePath);
criticNetwork = addLayers(criticNetwork,actionPath);
criticNetwork = addLayers(criticNetwork,commonPath);
criticNetwork = connectLayers(criticNetwork,'CriticStateFC2','add/in1');
criticNetwork = connectLayers(criticNetwork,'CriticActionFC1','add/in2');
criticOptions = rlRepresentationOptions('LearnRate',1e-03,'GradientThreshold',1);
critic = rlRepresentation(criticNetwork,obsInfo,actInfo,...
actorNetwork = [
imageInputLayer([numObservations 1 1],'Normalization','none','Name','observation')
actorOptions = rlRepresentationOptions('LearnRate',5e-04,'GradientThreshold',1);
actor = rlRepresentation(actorNetwork,obsInfo,actInfo,...
agentOptions = rlDDPGAgentOptions(...
agentOptions.NoiseOptions.Variance = 0.4;
agentOptions.NoiseOptions.VarianceDecayRate = 1e-5;
agent = rlDDPGAgent(actor,critic,agentOptions);
maxepisodes = 2000;
maxsteps = ceil(Tf/Ts);
trainingOptions = rlTrainingOptions(...
doTraining = false;
if doTraining
% Train the agent.
trainingStats = train(agent,env,trainingOptions);
% Load pretrained agent for the example.
simOptions = rlSimulationOptions('MaxSteps',500);
experience = sim(env,agent,simOptions);
% bdclose(mdl)
Here is my generated policy function code:
function action1 = evaluatePolicy(observation1)
% Reinforcement Learning Toolbox
% Generated on: 17-Oct-2019 13:34:45
action1 = localEvaluate(observation1);
%% Local Functions
function action1 = localEvaluate(observation1)
persistent policy
if isempty(policy)
policy = coder.loadDeepLearningNetwork('agentData.mat','policy');
action1 = predict(policy,observation1);
The error I get is the following:
Simulink does not have enough information to determine output sizes for this block. If you think the errors below are inaccurate, try specifying types for the block inputs and/or sizes for the block outputs.
Undefined function or variable 'dltargets'. P-code function 'DeepLearningNetwork.p' produced an error.
Function call failed. Function 'loadDeepLearningNetwork.m' (#95.3569.3643), line 100, column 15: "coder.DeepLearningNetwork(coder.const(matfile), coder.const(''), param{:})" Launch diagnostic report.
Function call failed. Function 'MATLAB Function' (#173.295.353), line 13, column 14: "coder.loadDeepLearningNetwork('agentData.mat','agentData')" Launch diagnostic report.
Persistent variable 'agentData' must be assigned before it is used. The only exception is a check using 'isempty(agentData)' that can be performed prior to assignment. Function 'MATLAB Function' (#173.377.386), line 15, column 19: "agentData" Launch diagnostic report.
Function call failed. Function 'MATLAB Function' (#173.140.167), line 7, column 11: "localEvaluate(observation1)" Launch diagnostic report.
Errors occurred during parsing of MATLAB function 'rlCartPoleSimscapeModel1/MATLAB Function'
Simulink cannot determine sizes and/or types of the outputs for block 'rlCartPoleSimscapeModel1/MATLAB Function' due to errors in the block body, or limitations of the underlying analysis. The errors might be inaccurate. Fix the indicated errors, or explicitly specify sizes and/or types for all block outputs.
Simulink cannot determine sizes and/or types of the outputs for block 'rlCartPoleSimscapeModel1/MATLAB Function' due to errors in the block body, or limitations of the underlying analysis. The errors might be inaccurate. Fix the indicated errors, or explicitly specify sizes and/or types for all block outputs.
Any feedback is much appreciated.
Thank you.
Rene Titze
Rene Titze on 14 Feb 2020
in the Function Block i take this code:
function y = predictTau(u)
policy = evalin('base', 'policy');
y = single(0.0);
y = predict(policy,u);

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Answers (5)

Sandra Diaz Segura
Sandra Diaz Segura on 6 Aug 2020
Any answers?, I think this is a legit question with enough information to be solved.
And given the lack of information in the RL user guide, MATLAB should have an answer to this!

Francisco Sanchez
Francisco Sanchez on 21 Oct 2019
I also had this error. Instead of solving it I went around it by using an "Interpreted MATLAB Fcn" block pointing to the .m generated by the "generatePolicyFunction" function of the RL toolbox. It does work although perhaps its not the fastest way.
H. M.
H. M. on 20 Oct 2022
Hi Rajesh
Did the problem you faced solved. If yes, could you provide me the solution.
I faced the same problem.

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krishna teja
krishna teja on 11 Feb 2020
use reshape block to set observation vector to column vector before feeding to matlab interpreter block

SomeMatlabUser on 20 Feb 2020
Is there any Update (maybe from Mathworks itself) to actually solve this problem? I am trying to get my model working with code generation. Using the interpreted matlab function block is not suitable and the documentation by mathworks is lacking at this point.
  1 Comment
Sviatoslav Klos
Sviatoslav Klos on 3 Mar 2020
I already settled this issue to generate code in MATLAB. But I did not solve it for code generation in SIMULINK.

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Kishen Mahadevan
Kishen Mahadevan on 15 Mar 2021
Starting R2020b, the 'Predict' block and the 'MATLAB Function' block allow using pre-trained networks including Reinforcement Learning policies in Simulink to perform inference. You can use either of the blocks to replace the RL Agent block in your model to perform inference in Simulink.
Please refer to this MATLAB Answers post for more information.
Hope it help!

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