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rlTRPOAgent

Trust region policy optimization reinforcement learning agent

Description

Trust region policy optimization (TRPO) is a model-free, online, on-policy, policy gradient reinforcement learning method. This algorithm prevents significant performance drops compared to standard policy gradient methods by keeping the updated policy within a trust region close to the current policy. The action space can be either discrete or continuous.

For more information on TRPO agents, see Trust Region Policy Optimization Agents. For more information on the different types of reinforcement learning agents, see Reinforcement Learning Agents.

Creation

Description

Create Agent from Observation and Action Specifications

example

agent = rlTRPOAgent(observationInfo,actionInfo) creates a trust region policy optimization (TRPO) agent for an environment with the given observation and action specifications, using default initialization options. The actor and critic representations in the agent use default deep neural networks built from the observation specification observationInfo and the action specification actionInfo.

example

agent = rlTRPOAgent(observationInfo,actionInfo,initOpts) creates a TRPO agent for an environment with the given observation and action specifications. The agent uses default networks configured using options specified in the initOpts object. TRPO agents do not support recurrent neural networks. For more information on the initialization options, see rlAgentInitializationOptions.

Create Agent from Actor and Critic Representations

example

agent = rlTRPOAgent(actor,critic) creates a TRPO agent with the specified actor and critic, using the default options for the agent.

Specify Agent Options

example

agent = rlTRPOAgent(___,agentOptions) creates a TRPO agent and sets the AgentOptions property to the agentOptions input argument. Use this syntax after any of the input arguments in the previous syntaxes.

Input Arguments

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Observation specifications, specified as a reinforcement learning specification object or an array of specification objects defining properties such as dimensions, data type, and names of the observation signals.

You can extract observationInfo from an existing environment or agent using getObservationInfo. You can also construct the specifications manually using rlFiniteSetSpec or rlNumericSpec.

Action specifications, specified as a reinforcement learning specification object defining properties such as dimensions, data type, and names of the action signals.

For a discrete action space, you must specify actionInfo as an rlFiniteSetSpec object.

For a continuous action space, you must specify actionInfo as an rlNumericSpec object.

You can extract actionInfo from an existing environment or agent using getActionInfo. You can also construct the specification manually using rlFiniteSetSpec or rlNumericSpec.

Agent initialization options, specified as an rlAgentInitializationOptions object.

TRPO agents do not support recurrent neural networks. Therefore initOpts.UseRNNmust be false.

Actor network representation for the policy, specified as an rlStochasticActorRepresentation object. For more information on creating actor representations, see Create Policy and Value Function Representations.

Actor representations for TRPO agents use only the UseDevice option in an rlRepresentationOptions object. Therefore, if you use a CPU for deep neural network computations, you can use the default representation options.

Critic network representation for estimating the discounted long-term reward, specified as an rlValueRepresentation. For more information on creating critic representations, see Create Policy and Value Function Representations.

Properties

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Agent options, specified as an rlTRPOAgentOptions object.

Object Functions

trainTrain reinforcement learning agents within a specified environment
simSimulate trained reinforcement learning agents within specified environment
getActionObtain action from agent or actor representation given environment observations
getActorGet actor representation from reinforcement learning agent
setActorSet actor representation of reinforcement learning agent
getCriticGet critic representation from reinforcement learning agent
setCriticSet critic representation of reinforcement learning agent
generatePolicyFunctionCreate function that evaluates trained policy of reinforcement learning agent

Examples

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Create an environment with a discrete action space, and obtain its observation and action specifications. For this example, load the environment used in the example Create Agent Using Deep Network Designer and Train Using Image Observations. This environment has two observations: a 50-by-50 grayscale image and a scalar (the angular velocity of the pendulum). The action is a scalar with five possible elements (a torque of either -2, -1, 0, 1, or 2 Nm applied to a swinging pole).

% load predefined environment
env = rlPredefinedEnv("SimplePendulumWithImage-Discrete");

Obtain the observation and action specifications for this environment.

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

The agent creation function initializes the actor and critic networks randomly. You can ensure reproducibility by fixing the seed of the random generator. To do so, uncomment the following line.

% rng(0)

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

agent = rlTRPOAgent(obsInfo,actInfo);

To check your agent, use getAction to return the action from a random observation.

getAction(agent,{rand(obsInfo(1).Dimension),rand(obsInfo(2).Dimension)})
ans = 1x1 cell array
    {[-2]}

You can now test and train the agent within the environment.

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 Swing Up and Balance Pendulum with Image Observation. This environment has two observations: a 50-by-50 grayscale image and a scalar (the angular velocity of the pendulum). The action is a scalar representing a torque ranging continuously from -2 to 2 Nm.

env = rlPredefinedEnv("SimplePendulumWithImage-Continuous");

Obtain observation and action specifications for this environment.

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

Create an agent initialization options object, specifying that each hidden fully connected layer in the network must have 128 neurons.

initOpts = rlAgentInitializationOptions('NumHiddenUnit',128);

The agent creation function initializes the actor and critic networks randomly. You can ensure reproducibility by fixing the seed of the random generator. To do so, uncomment the following line.

% rng(0)

Create a TRPO agent from the environment observation and action specifications using the specified initialization options.

agent = rlTRPOAgent(obsInfo,actInfo,initOpts);

Reduce the critic learning rate to 1e-3.

critic = getCritic(agent);
critic.Options.LearnRate = 1e-3;
agent  = setCritic(agent,critic);

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

actorNet = getModel(getActor(agent));
criticNet = getModel(getCritic(agent));

You can verify that the networks have 128 units in their hidden fully connected layers. For example, display the layers of the critic network.

criticNet.Layers
ans = 
  11x1 Layer array with layers:

     1   'input_1'        Image Input       50x50x1 images
     2   'conv_1'         Convolution       64 3x3x1 convolutions with stride [1  1] and padding [0  0  0  0]
     3   'relu_input_1'   ReLU              ReLU
     4   'fc_1'           Fully Connected   128 fully connected layer
     5   'input_2'        Feature Input     1 features
     6   'fc_2'           Fully Connected   128 fully connected layer
     7   'concat'         Concatenation     Concatenation of 2 inputs along dimension 1
     8   'relu_body'      ReLU              ReLU
     9   'fc_body'        Fully Connected   128 fully connected layer
    10   'body_output'    ReLU              ReLU
    11   'output'         Fully Connected   1 fully connected layer

To check your agent, use getAction to return the action from a random observation.

getAction(agent,{rand(obsInfo(1).Dimension),rand(obsInfo(2).Dimension)})
ans = 1x1 cell array
    {[0.9228]}

You can now test and train the agent within the environment.

Create an environment interface, and obtain its observation and action specifications.

env = rlPredefinedEnv("CartPole-Discrete");
obsInfo = getObservationInfo(env);
actInfo = getActionInfo(env);

Create a critic representation.

% Create the network to be used as approximator in the critic.
criticNetwork = [
    featureInputLayer(4,'Normalization','none','Name','state')
    fullyConnectedLayer(1,'Name','CriticFC')];

% Set options for the critic.
criticOpts = rlRepresentationOptions('LearnRate',8e-3,'GradientThreshold',1);

% Create the critic.
critic = rlValueRepresentation(criticNetwork,obsInfo,'Observation',{'state'},criticOpts);

Create an actor representation.

% Create the network to be used as approximator in the actor.
actorNetwork = [
    featureInputLayer(4,'Normalization','none','Name','state')
    fullyConnectedLayer(2,'Name','action')];

% Create the actor.
actor = rlStochasticActorRepresentation(actorNetwork,obsInfo,actInfo,...
    'Observation',{'state'});

Specify agent options, and create a TRPO agent using the environment, actor, and critic.

agentOpts = rlTRPOAgentOptions(...
    'ExperienceHorizon',1024, ...
    'DiscountFactor',0.95);
agent = rlTRPOAgent(actor,critic,agentOpts)
agent = 
  rlTRPOAgent with properties:

    AgentOptions: [1x1 rl.option.rlTRPOAgentOptions]

To check your agent, use getAction to return the action from a random observation.

getAction(agent,{rand(4,1)})
ans = 1x1 cell array
    {[-10]}

You can now test and train the agent against the environment.

Create an environment with a continuous action space, and obtain its observation and action specifications. For this example, load the double integrator continuous action space environment used in the example Train DDPG Agent to Control Double Integrator System. The observation from the environment is a vector containing the position and velocity of a mass. The action is a scalar representing a force applied to the mass, ranging continuously from -2 to 2 Newton.

env = rlPredefinedEnv("DoubleIntegrator-Continuous");
obsInfo = getObservationInfo(env)
obsInfo = 
  rlNumericSpec with properties:

     LowerLimit: -Inf
     UpperLimit: Inf
           Name: "states"
    Description: "x, dx"
      Dimension: [2 1]
       DataType: "double"

actInfo = getActionInfo(env)
actInfo = 
  rlNumericSpec with properties:

     LowerLimit: -Inf
     UpperLimit: Inf
           Name: "force"
    Description: [0x0 string]
      Dimension: [1 1]
       DataType: "double"

Since the action must be contained in a limited range, set the upper and lower limit of the action signal accordingly. You must do so when the network representation for the actor has a nonlinear output layer that must be scaled to produce an output in the desired range.

actInfo.LowerLimit=-2;
actInfo.UpperLimit=2;

Create a critic representation. TRPO agents use a rlValueRepresentation for the critic. For continuous observation spaces, you can use either a deep neural network or a custom basis representation. For this example, create a deep neural network as the underlying approximator.

% create the network to be used as approximator in the critic
% it must take the observation signal as input and produce a scalar value
criticNet = [
    imageInputLayer([obsInfo.Dimension 1],'Normalization','none','Name','state')
    fullyConnectedLayer(10,'Name', 'fc_in')
    reluLayer('Name', 'relu')
    fullyConnectedLayer(1,'Name','out')];

% set some training options for the critic
criticOpts = rlRepresentationOptions('LearnRate',8e-3,'GradientThreshold',1);

% create the critic representation from the network
critic = rlValueRepresentation(criticNet,obsInfo,'Observation',{'state'},criticOpts);

TRPO agents use a rlStochasticActorRepresentation. For continuous action spaces, stochastic actors can only use a neural network approximator.

The observation input (here called myobs) must accept a two-dimensional vector, as specified in obsInfo. The output (here called myact) must also be a two-dimensional vector (twice the number of dimensions specified in actInfo). The elements of the output vector represent, in sequence, all the means and all the standard deviations of every action (in this case there is only one mean value and one standard deviation).

The fact that standard deviations must be non-negative while mean values must fall within the output range means that the network must have two separate paths. The first path is for the mean values, and any output nonlinearity must be scaled so that it can produce outputs in the output range. The second path is for the standard deviations, and you must use a softplus or relu layer to enforce non-negativity.

% input path layers (2 by 1 input and a 1 by 1 output)
inPath = [ 
    imageInputLayer([obsInfo.Dimension 1], 'Normalization','none','Name','state')
    fullyConnectedLayer(10,'Name', 'ip_fc')   % 10 by 1 output
    reluLayer('Name', 'ip_relu')              % nonlinearity
    fullyConnectedLayer(1,'Name','ip_out') ]; % 1 by 1 output

% path layers for mean value (1 by 1 input and 1 by 1 output)
% using scalingLayer to scale the range
meanPath = [
    fullyConnectedLayer(15,'Name', 'mp_fc1') % 15 by 1 output
    reluLayer('Name', 'mp_relu')             % nonlinearity
    fullyConnectedLayer(1,'Name','mp_fc2');  % 1 by 1 output
    tanhLayer('Name','tanh');                % output range: (-1,1)
    scalingLayer('Name','mp_out','Scale',actInfo.UpperLimit) ]; % output range: (-2N,2N)

% path layers for standard deviation (1 by 1 input and output)
% using softplus layer to make it non negative
sdevPath = [
    fullyConnectedLayer(15,'Name', 'vp_fc1') % 15 by 1 output
    reluLayer('Name', 'vp_relu')             % nonlinearity
    fullyConnectedLayer(1,'Name','vp_fc2');  % 1 by 1 output
    softplusLayer('Name', 'vp_out') ];       % output range: (0,+Inf)

% conctatenate two inputs (along dimension #3) to form a single (2 by 1) output layer
outLayer = concatenationLayer(1,2,'Name','mean&sdev');

% add layers to layerGraph network object
actorNet = layerGraph(inPath);
actorNet = addLayers(actorNet,meanPath);
actorNet = addLayers(actorNet,sdevPath);
actorNet = addLayers(actorNet,outLayer);

% connect layers: you must conect the mean value path to the first input of the concatenation layer
actorNet = connectLayers(actorNet,'ip_out','mp_fc1/in');     % connect output of inPath to meanPath input
actorNet = connectLayers(actorNet,'ip_out','vp_fc1/in');     % connect output of inPath to sdevPath input
actorNet = connectLayers(actorNet,'mp_out','mean&sdev/in1'); % connect output of meanPath to mean&sdev input #1
actorNet = connectLayers(actorNet,'vp_out','mean&sdev/in2'); % connect output of sdevPath to mean&sdev input #2

% plot network 
plot(actorNet)

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

Create the stochastic actor representation using the deep neural network actorNet.

actor = rlStochasticActorRepresentation(actorNet,obsInfo,actInfo,...
    'Observation',{'state'});

Specify agent options, and create a TRPO agent using the actor, critic and agent options.

agentOpts = rlTRPOAgentOptions(...
    'ExperienceHorizon',1024, ...
    'DiscountFactor',0.95);
agent = rlTRPOAgent(actor,critic,agentOpts)
agent = 
  rlTRPOAgent with properties:

    AgentOptions: [1x1 rl.option.rlTRPOAgentOptions]

To check your agent, use getAction to return the action from a random observation.

getAction(agent,{rand(2,1)})
ans = 1x1 cell array
    {[0.6668]}

You can now test and train the agent within the environment.

Tips

  • For continuous action spaces, this agent does not enforce the constraints set by the action specification. In this case, you must enforce action space constraints within the environment.

  • While tuning the learning rate of the actor network is necessary for PPO agents, it is not necessary for TRPO agents.

  • For high-dimensional observations, such as for images, it is recommended to use PPO, SAC, or TD3 agents.

Introduced in R2021b