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rlDQNAgent

Deep Q-network reinforcement learning agent

Description

The deep Q-network (DQN) algorithm is a model-free, online, off-policy reinforcement learning method. A DQN agent is a value-based reinforcement learning agent that trains a critic to estimate the return or future rewards. DQN is a variant of Q-learning, and it operates only within discrete action spaces.

For more information, Deep Q-Network 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 = rlDQNAgent(observationInfo,actionInfo) creates a DQN agent for an environment with the given observation and action specifications, using default initialization options. The critic representation in the agent uses a default multi-output Q-value deep neural network built from the observation specification observationInfo and the action specification actionInfo.

example

agent = rlDQNAgent(observationInfo,actionInfo,initOpts) creates a DQN agent for an environment with the given observation and action specifications. The agent uses a default network configured using options specified in the initOpts object. For more information on the initialization options, see rlAgentInitializationOptions.

Create Agent from Critic Representation

agent = rlDQNAgent(critic) creates a DQN agent with the specified critic network using a default option set for a DQN agent.

Specify Agent Options

example

agent = rlDQNAgent(critic,agentOptions) creates a DQN agent with the specified critic network 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.

Since a DDPG agent operates in a discrete action space, you must specify actionInfo as an rlFiniteSetSpec object.

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

Agent initialization options, specified as an rlAgentInitializationOptions object.

Critic network representation, specified as an rlQValueRepresentation object. For more information on creating critic representations, see Create Policy and Value Function Representations.

Your critic representation can use a recurrent neural network as its function approximator. However, only the multi-output Q-value function representation supports recurrent neural networks. For an example, see Create DQN Agent with Recurrent Neural Network.

Properties

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Agent options, specified as an rlDQNAgentOptions object.

Experience buffer, specified as an ExperienceBuffer object. During training the agent stores each of its experiences (S,A,R,S') in a buffer. Here:

  • S is the current observation of the environment.

  • A is the action taken by the agent.

  • R is the reward for taking action A.

  • S' is the next observation after taking action A.

For more information on how the agent samples experience from the buffer during training, see Deep Q-Network Agents.

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 observation and action specifications
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 deep Q-network agent from the environment observation and action specifications.

agent = rlDQNAgent(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 = 1

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

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 observation and action specifications
obsInfo = getObservationInfo(env);
actInfo = getActionInfo(env);

Create an agent initialization option object, specifying that each hidden fully connected layer in the network must have 128 neurons (instead of the default number, 256).

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 policy gradient agent from the environment observation and action specifications.

agent = rlPGAgent(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 network from both the critic.

criticNet = getModel(getCritic(agent));

The default DQN agent uses a multi-output Q-value critic approximator. A multi-output approximator has observations as inputs and state-action values as outputs. Each output element represents the expected cumulative long-term reward for taking the corresponding discrete action from the state indicated by the observation inputs.

Display the layers of the critic network, and verify that each hidden fully connected layer has 128 neurons

criticNet.Layers
ans = 
  12x1 Layer array with layers:

     1   'concat'               Concatenation       Concatenation of 2 inputs along dimension 3
     2   'relu_body'            ReLU                ReLU
     3   'fc_body'              Fully Connected     128 fully connected layer
     4   'body_output'          ReLU                ReLU
     5   'input_1'              Image Input         50x50x1 images
     6   'conv_1'               Convolution         64 3x3x1 convolutions with stride [1  1] and padding [0  0  0  0]
     7   'relu_input_1'         ReLU                ReLU
     8   'fc_1'                 Fully Connected     128 fully connected layer
     9   'input_2'              Image Input         1x1x1 images
    10   'fc_2'                 Fully Connected     128 fully connected layer
    11   'output'               Fully Connected     1 fully connected layer
    12   'RepresentationLoss'   Regression Output   mean-squared-error

Plot the critic network

plot(criticNet)

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 interface and obtain its observation and action specifications. For this example load the predefined environment used for the Train DQN Agent to Balance Cart-Pole System example. This environment has a continuous four-dimensional observation space (the positions and velocities of both cart and pole) and a discrete one-dimensional action space consisting on the application of two possible forces, -10N or 10N.

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

% get observation and action specification objects
obsInfo = getObservationInfo(env);
actInfo = getActionInfo(env);

For an agent with a discrete action space, you have the option to create a multi-output critic representation, which is generally more efficient than a comparable single-output critic representation.

A multi-output critic has only the observation as input, and an output vector having as many elements as the number of possible discrete actions. Each output element represents the expected cumulative long-term reward following from the observation given as input, when the corresponding discrete action is taken.

Create the multi-output critic representation using a deep neural network approximator.

% create a deep neural network approximator 
% the observation input layer must have 4 elements (obsInfo.Dimension(1))
% the action output layer must have 2 elements (length(actInfo.Elements))
dnn = [
    imageInputLayer([obsInfo.Dimension(1) 1 1], 'Normalization', 'none', 'Name', 'state')
    fullyConnectedLayer(24, 'Name', 'CriticStateFC1')
    reluLayer('Name', 'CriticRelu1')
    fullyConnectedLayer(24, 'Name', 'CriticStateFC2')
    reluLayer('Name','CriticCommonRelu')
    fullyConnectedLayer(length(actInfo.Elements), 'Name', 'output')];

% set some options for the critic
criticOpts = rlRepresentationOptions('LearnRate',0.01,'GradientThreshold',1);

% create the critic based on the network approximator
critic = rlQValueRepresentation(dnn,obsInfo,actInfo,'Observation',{'state'},criticOpts);

Specify agent options, and create a DQN agent using the critic.

agentOpts = rlDQNAgentOptions(...
    'UseDoubleDQN',false, ...    
    'TargetUpdateMethod',"periodic", ...
    'TargetUpdateFrequency',4, ...   
    'ExperienceBufferLength',100000, ...
    'DiscountFactor',0.99, ...
    'MiniBatchSize',256);

agent = rlDQNAgent(critic,agentOpts)
agent = 
  rlDQNAgent with properties:

        AgentOptions: [1x1 rl.option.rlDQNAgentOptions]
    ExperienceBuffer: [1x1 rl.util.ExperienceBuffer]

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

getAction(agent,{rand(4,1)})
ans = 10

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

Create an environment interface and obtain its observation and action specifications. For this example load the predefined environment used for the Train DQN Agent to Balance Cart-Pole System example. This environment has a continuous four-dimensional observation space (the positions and velocities of both cart and pole) and a discrete one-dimensional action space consisting on the application of two possible forces, -10N or 10N.

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

% get observation and specification info
obsInfo = getObservationInfo(env);
actInfo = getActionInfo(env);

Create a single-output critic representation using a deep neural network approximator. It must have both observations and action as input layers, and a single scalar output representing the expected cumulative long-term reward following from the given observation and action.

% create a deep neural network approximator 
% the observation input layer must have 4 elements (obsInfo.Dimension(1))
% the action input layer must have 1 element (actInfo.Dimension(1))
% the output must be a scalar
statePath = [
    featureInputLayer(obsInfo.Dimension(1), 'Normalization', 'none', 'Name', 'state')
    fullyConnectedLayer(24, 'Name', 'CriticStateFC1')
    reluLayer('Name', 'CriticRelu1')
    fullyConnectedLayer(24, 'Name', 'CriticStateFC2')];
actionPath = [
    featureInputLayer(actInfo.Dimension(1), 'Normalization', 'none', 'Name', 'action')
    fullyConnectedLayer(24, 'Name', 'CriticActionFC1')];
commonPath = [
    additionLayer(2,'Name', 'add')
    reluLayer('Name','CriticCommonRelu')
    fullyConnectedLayer(1, 'Name', 'output')];
criticNetwork = layerGraph(statePath);
criticNetwork = addLayers(criticNetwork, actionPath);
criticNetwork = addLayers(criticNetwork, commonPath);    
criticNetwork = connectLayers(criticNetwork,'CriticStateFC2','add/in1');
criticNetwork = connectLayers(criticNetwork,'CriticActionFC1','add/in2');

% set some options for the critic
criticOpts = rlRepresentationOptions('LearnRate',0.01,'GradientThreshold',1);

% create the critic based on the network approximator
critic = rlQValueRepresentation(criticNetwork,obsInfo,actInfo,...
    'Observation',{'state'},'Action',{'action'},criticOpts);

Specify agent options, and create a DQN agent using the critic.

agentOpts = rlDQNAgentOptions(...
    'UseDoubleDQN',false, ...    
    'TargetUpdateMethod',"periodic", ...
    'TargetUpdateFrequency',4, ...   
    'ExperienceBufferLength',100000, ...
    'DiscountFactor',0.99, ...
    'MiniBatchSize',256);

agent = rlDQNAgent(critic,agentOpts)
agent = 
  rlDQNAgent with properties:

        AgentOptions: [1x1 rl.option.rlDQNAgentOptions]
    ExperienceBuffer: [1x1 rl.util.ExperienceBuffer]

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

getAction(agent,{rand(4,1)})
ans = 10

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

Create an environment and obtain observation and action information.

env = rlPredefinedEnv('CartPole-Discrete');
obsInfo = getObservationInfo(env);
actInfo = getActionInfo(env);
numObs = obsInfo.Dimension(1);
numDiscreteAct = numel(actInfo.Elements);

Create a recurrent deep neural network for your critic. To create a recurrent neural network, use a sequenceInputLayer as the input layer and include an lstmLayer as one of the other network layers.

For DQN agents, only the multi-output Q-value function representation supports recurrent neural networks.

criticNetwork = [
    sequenceInputLayer(numObs,'Normalization','none','Name','state')
    fullyConnectedLayer(50, 'Name', 'CriticStateFC1')
    reluLayer('Name','CriticRelu1')
    lstmLayer(20,'OutputMode','sequence','Name','CriticLSTM');
    fullyConnectedLayer(20,'Name','CriticStateFC2')
    reluLayer('Name','CriticRelu2')
    fullyConnectedLayer(numDiscreteAct,'Name','output')];

Create a representation for your critic using the recurrent neural network.

criticOptions = rlRepresentationOptions('LearnRate',1e-3,'GradientThreshold',1);
critic = rlQValueRepresentation(criticNetwork,obsInfo,actInfo,...
    'Observation','state',criticOptions);

Specify options for creating the DQN agent. To use a recurrent neural network, you must specify a SequenceLength greater than 1.

agentOptions = rlDQNAgentOptions(...
    'UseDoubleDQN',false, ...
    'TargetSmoothFactor',5e-3, ...
    'ExperienceBufferLength',1e6, ...
    'SequenceLength',20);
agentOptions.EpsilonGreedyExploration.EpsilonDecay = 1e-4;
agent = rlDQNAgent(critic,agentOptions);
Introduced in R2019a