rlDQNAgentOptions

Options for DQN agent

Since R2019a

Description

Use an rlDQNAgentOptions object to specify options for deep Q-network (DQN) agents. To create a DQN agent, use rlDQNAgent.

For more information, see Deep Q-Network (DQN) Agents.

For more information on the different types of reinforcement learning agents, see Reinforcement Learning Agents.

Creation

Syntax

opt = rlDQNAgentOptions

opt = rlDQNAgentOptions(Name=Value)

Description

opt = rlDQNAgentOptions creates an options object for use as an argument when creating a DQN agent using all default settings. You can modify the object properties using dot notation.

opt = rlDQNAgentOptions(Name=Value) creates the options set opt and sets its properties using one or more name-value arguments. For example, rlDQNAgentOptions(DiscountFactor=0.95) creates an options set with a discount factor of 0.95. You can specify multiple name-value arguments.

Properties

UseDoubleDQN — Option to use double DQN

true (default) | false

Option to use double DQN for value function target updates, specified as a logical value. For more information, see Deep Q-Network (DQN) Agents.

Example: UseDoubleDQN=false

EpsilonGreedyExploration — Options for epsilon-greedy exploration

EpsilonGreedyExploration object

Options for epsilon-greedy exploration, specified as an EpsilonGreedyExploration object with the following properties.

Property	Description	Default Value
Epsilon	Probability threshold to either randomly select an action or select the action that maximizes the state-action value function. A larger value of Epsilon means that the agent randomly explores the action space at a higher rate.	1
EpsilonMin	Minimum value of Epsilon	0.01
EpsilonDecay	Decay rate	0.0050

At the end of each training time step, if Epsilon is greater than EpsilonMin, then it is updated using the following formula.

Epsilon = Epsilon*(1-EpsilonDecay)

Note that Epsilon is conserved between the end of an episode and the start of the next one. Therefore, it keeps on uniformly decreasing over multiple episodes until it reaches EpsilonMin.

If your agent converges on local optima too quickly, you can promote agent exploration by increasing Epsilon.

To specify exploration options, use dot notation after creating the rlDQNAgentOptions object opt. For example, set the epsilon value to 0.9.

opt.EpsilonGreedyExploration.Epsilon = 0.9;

CriticOptimizerOptions — Critic optimizer options

rlOptimizerOptions object

Critic optimizer options, specified as an rlOptimizerOptions object. It allows you to specify training parameters of the critic approximator such as learning rate, gradient threshold, as well as the optimizer algorithm and its parameters. For more information, see rlOptimizerOptions and rlOptimizer.

Example: CriticOptimizerOptions = rlOptimizerOptions(LearnRate=5e-3)

BatchDataRegularizerOptions — Batch data regularizer options

[] (default) | rlBehaviorCloningRegularizerOptions object

Batch data regularizer options, specified as an rlBehaviorCloningRegularizerOptions object. These options are typically used to train the agent offline, from existing data. If you leave this option empty, no regularizer is used.

For more information, see rlBehaviorCloningRegularizerOptions.

Example: BatchDataRegularizerOptions = rlBehaviorCloningRegularizerOptions(BehaviorCloningRegularizerWeight=10)

TargetSmoothFactor — Smoothing factor for target critic updates

1e-3 (default) | positive scalar less than or equal to 1

Smoothing factor for target critic updates, specified as a positive scalar less than or equal to 1. For more information, see Target Update Methods.

Example: TargetSmoothFactor=1e-2

TargetUpdateFrequency — Number of steps between target critic updates

1 (default) | positive integer

Number of steps between target critic updates, specified as a positive integer. For more information, see Target Update Methods.

Example: TargetUpdateFrequency=5

ResetExperienceBufferBeforeTraining — Option for clearing the experience buffer

false (default) | true

Option for clearing the experience buffer before training, specified as a logical value.

Example: ResetExperienceBufferBeforeTraining=true

SequenceLength — Maximum batch-training trajectory length when using RNN

1 (default) | positive integer

Maximum batch-training trajectory length when using a recurrent neural network for the critic, specified as a positive integer. This value must be greater than 1 when using a recurrent neural network for the critic and 1 otherwise.

Example: SequenceLength=4

MiniBatchSize — Size of random experience mini-batch

64 (default) | positive integer

Size of random experience mini-batch, specified as a positive integer. During each training episode, the agent randomly samples experiences from the experience buffer when computing gradients for updating the critic properties. Large mini-batches reduce the variance when computing gradients but increase the computational effort.

When using a recurrent neural network for the critic, MiniBatchSize is the number of experience trajectories in a batch, where each trajectory has length equal to SequenceLength.

Example: MiniBatchSize=128

NumStepsToLookAhead — Number of future rewards used to estimate the value of the policy

1 (default) | positive integer

Number of future rewards used to estimate the value of the policy, specified as a positive integer. Specifically, ifNumStepsToLookAhead is equal to N, the target value of the policy at a given step is calculated adding the rewards for the following N steps and the discounted estimated value of the state that caused the N-th reward. This target is also called N-step return.

Note

When using a recurrent neural network for the critic, NumStepsToLookAhead must be 1.

For more information, see [1], Chapter 7.

Example: NumStepsToLookAhead=3

ExperienceBufferLength — Experience buffer size

10000 (default) | positive integer

Experience buffer size, specified as a positive integer. During training, the agent computes updates using a mini-batch of experiences randomly sampled from the buffer.

Example: ExperienceBufferLength=1e6

SampleTime — Sample time of agent

1 (default) | positive scalar | -1

Sample time of agent, specified as a positive scalar or as -1. Setting this parameter to -1 allows for event-based simulations.

Within a Simulink^® environment, the RL Agent block in which the agent is specified to execute every SampleTime seconds of simulation time. If SampleTime is -1, the block inherits the sample time from its parent subsystem.

Within a MATLAB^® environment, the agent is executed every time the environment advances. In this case, SampleTime is the time interval between consecutive elements in the output experience returned by sim or train. If SampleTime is -1, the time interval between consecutive elements in the returned output experience reflects the timing of the event that triggers the agent execution.

Example: SampleTime=-1

DiscountFactor — Discount factor

0.99 (default) | positive scalar less than or equal to 1

Discount factor applied to future rewards during training, specified as a positive scalar less than or equal to 1.

Example: DiscountFactor=0.9

Object Functions

rlDQNAgent

Deep Q-network (DQN) reinforcement learning agent

Examples

Create DQN Agent Options Object

Create an rlDQNAgentOptions object that specifies the agent mini-batch size.

opt = rlDQNAgentOptions(MiniBatchSize=48)

opt = 
  rlDQNAgentOptions with properties:

                             SampleTime: 1
                         DiscountFactor: 0.9900
               EpsilonGreedyExploration: [1x1 rl.option.EpsilonGreedyExploration]
                 ExperienceBufferLength: 10000
                          MiniBatchSize: 48
                         SequenceLength: 1
                 CriticOptimizerOptions: [1x1 rl.option.rlOptimizerOptions]
                    NumStepsToLookAhead: 1
                           UseDoubleDQN: 1
                     TargetSmoothFactor: 1.0000e-03
                  TargetUpdateFrequency: 1
            BatchDataRegularizerOptions: []
    ResetExperienceBufferBeforeTraining: 0
                             InfoToSave: [1x1 struct]

You can modify options using dot notation. For example, set the agent sample time to 0.5.

opt.SampleTime = 0.5;

References

[1] Sutton, Richard S., and Andrew G. Barto. Reinforcement Learning: An Introduction. Second edition. Adaptive Computation and Machine Learning. Cambridge, Mass: The MIT Press, 2018.

Version History

Introduced in R2019a

R2022a: The default value of the ResetExperienceBufferBeforeTraining property has changed

The default value of the ResetExperienceBufferBeforeTraining has changed from true to false.

When creating a new DQN agent, if you want to clear the experience buffer before training, you must specify ResetExperienceBufferBeforeTraining as true. For example, before training, set the property using dot notation.

agent.AgentOptions.ResetExperienceBufferBeforeTraining = true;

Alternatively, you can set the property to true in an rlDQNAgentOptions object and use this object to create the DQN agent.

R2020a: Target update method settings for DQN agents have changed

Target update method settings for DQN agents have changed. The following changes require updates to your code:

• The TargetUpdateMethod option has been removed. Now, DQN agents determine the target update method based on the TargetUpdateFrequency and TargetSmoothFactor option values.

• The default value of TargetUpdateFrequency has changed from 4 to 1.

To use one of the following target update methods, set the TargetUpdateFrequency and TargetSmoothFactor properties as indicated.

Update Method	TargetUpdateFrequency	TargetSmoothFactor
Smoothing	1	Less than 1
Periodic	Greater than 1	1
Periodic smoothing (new method in R2020a)	Greater than 1	Less than 1

The default target update configuration, which is a smoothing update with a TargetSmoothFactor value of 0.001, remains the same.

Update Code

This table shows some typical uses of rlDQNAgentOptions and how to update your code to use the new option configuration.

Not Recommended	Recommended
opt = rlDQNAgentOptions('TargetUpdateMethod',"smoothing");	opt = rlDQNAgentOptions;
opt = rlDQNAgentOptions('TargetUpdateMethod',"periodic");	opt = rlDQNAgentOptions; opt.TargetUpdateFrequency = 4; opt.TargetSmoothFactor = 1;
opt = rlDQNAgentOptions; opt.TargetUpdateMethod = "periodic"; opt.TargetUpdateFrequency = 5;	opt = rlDQNAgentOptions; opt.TargetUpdateFrequency = 5; opt.TargetSmoothFactor = 1;