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Get critic representation from reinforcement learning agent



critic = getCritic(agent) returns the critic representation object for the specified reinforcement learning agent.


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Assume that you have an existing trained reinforcement learning agent. For this example, load the trained agent from Train DDPG Agent to Control Double Integrator System.


Obtain the critic representation from the agent.

critic = getCritic(agent);

Obtain the learnable parameters from the critic.

params = getLearnableParameters(critic);

Modify the parameter values. For this example, simply multiply all of the parameters by 2.

modifiedParams = cellfun(@(x) x*2,params,'UniformOutput',false);

Set the parameter values of the critic to the new modified values.

critic = setLearnableParameters(critic,modifiedParams);

Set the critic in the agent to the new modified critic.

agent = setCritic(agent,critic);

Create an environment with a continuous action space and obtain its observation and action specifications. For this example, load the environment used in the example Train DDPG Agent to Control Double Integrator System.

Load the predefined environment.

env = rlPredefinedEnv("DoubleIntegrator-Continuous")
env = 
  DoubleIntegratorContinuousAction with properties:

             Gain: 1
               Ts: 0.1000
      MaxDistance: 5
    GoalThreshold: 0.0100
                Q: [2x2 double]
                R: 0.0100
         MaxForce: Inf
            State: [2x1 double]

Obtain observation and action specifications.

obsInfo = getObservationInfo(env);
actInfo = getActionInfo(env);

Create a PPO agent from the environment observation and action specifications.

agent = rlPPOAgent(obsInfo,actInfo);

To modify the deep neural networks within a reinforcement learning agent, you must first extract the actor and critic representations.

actor = getActor(agent);
critic = getCritic(agent);

Extract the deep neural networks from both the actor and critic representations.

actorNet = getModel(actor);
criticNet = getModel(critic);

The networks are dlnetwork objects. To view them using the plot function, you must convert them to layerGraph objects.

For example, view the actor network.


Figure contains an axes object. The axes object contains an object of type graphplot.

To validate a network, use analyzeNetwork. For example, validate the critic network.


You can modify the actor and critic networks and save them back to the agent. To modify the networks, you can use the Deep Network Designer app. To open the app for each network, use the following commands.


In Deep Network Designer, modify the networks. For example, you can add additional layers to your network. When you modify the networks, do not change the input and output layers of the networks returned by getModel. For more information on building networks, see Build Networks with Deep Network Designer.

To validate the modified network in Deep Network Designer, you must click on Analyze for dlnetwork, under the Analysis section. To export the modified network structures to the MATLAB® workspace, generate code for creating the new networks and run this code from the command line. Do not use the exporting option in Deep Network Designer. For an example that shows how to generate and run code, see Create Agent Using Deep Network Designer and Train Using Image Observations.

For this example, the code for creating the modified actor and critic networks is in createModifiedNetworks.m.


Each of the modified networks includes an additional fullyConnectedLayer and reluLayer in their output path. View the modified actor network.


Figure contains an axes object. The axes object contains an object of type graphplot.

After exporting the networks, insert the networks into the actor and critic representations.

actor = setModel(actor,modifiedActorNet);
critic = setModel(critic,modifiedCriticNet);

Finally, insert the modified actor and critic representations in the actor and critic objects.

agent = setActor(agent,actor);
agent = setCritic(agent,critic);

Input Arguments

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Reinforcement learning agent that contains a critic representation, specified as one of the following:

Output Arguments

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Critic representation object, returned as one of the following:

  • rlValueRepresentation object — Returned when agent is an rlACAgent, rlPGAgent, or rlPPOAgent object

  • rlQValueRepresentation object — Returned when agent is an rlQAgent, rlSARSAAgent, rlDQNAgent, rlDDPGAgent, or rlTD3Agent object with a single critic

  • Two-element row vector of rlQValueRepresentation objects — Returned when agent is an rlTD3Agent or rlSACAgent object with two critics

Introduced in R2019a