rlDQNAgentOptions

Options for DQN agent

Description

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

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

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

Properties

SampleTime — Sample time of agent

1 (default) | positive scalar | -1

Sample time of the agent, specified as a positive scalar or as -1.

Within a MATLAB^® environment, the agent is executed every time the environment advances, so, SampleTime does not affect the timing of the agent execution. If SampleTime is set to -1, in MATLAB environments, the time interval between consecutive elements in the returned output experience is considered equal to 1.

Within a Simulink^® environment, the RL Agent block that uses the agent object executes every SampleTime seconds of simulation time. If SampleTime is set to -1 the block inherits the sample time from its input signals. Set SampleTime to -1 when the block is a child of an event-driven subsystem.

Set SampleTime to a positive scalar when the block is not a child of an event-driven subsystem. Doing so ensures that the block executes at appropriate intervals when input signal sample times change due to model variations. If SampleTime is a positive scalar, this value is also the time interval between consecutive elements in the output experience returned by sim or train, regardless of the type of environment.

If SampleTime is set to -1, in Simulink environments, the time interval between consecutive elements in the returned output experience reflects the timing of the events that trigger the RL Agent block execution.

This property is shared between the agent and the agent options object within the agent. If you change this property in the agent options object, it also changes in the agent, and vice versa.

Example: SampleTime=-1

DiscountFactor — Discount factor

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

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

Example: DiscountFactor=0.9

EpsilonGreedyExploration — Options for epsilon-greedy exploration

EpsilonGreedyExploration object

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

Property	Description	Default Value
Epsilon	Initial value of the probability threshold to either randomly select an action or select the action that maximizes the state-action value function. A larger Epsilon value 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 each interaction with the environment (that is, at each training step), if Epsilon is greater than EpsilonMin, then it is updated using this formula.

Epsilon = Epsilon*(1-EpsilonDecay)

Epsilon is conserved between the end of an episode and the start of the next one. So, Epsilon decreases uniformly over multiple episodes until it reaches EpsilonMin.

If your agent converges on a local optimum too quickly, you can promote agent exploration by increasing the value of Epsilon.

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

opt.EpsilonGreedyExploration.Epsilon = 0.9;

Note

The Epsilon property of an EpsilonGreedyExploration object represents the initial value of Epsilon at the beginning of the first episode.

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

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

SequenceLength — Maximum batch-training trajectory length when using RNN

1 (default) | positive integer

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

Example: SequenceLength=4

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)

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

NumWarmStartSteps — Minimum number of samples to generate before learning starts

positive integer

Minimum number of samples to generate before learning starts. Use this option to ensure that learning takes place over a more diverse data set at the beginning of training. The default, and minimum, value is the value of MiniBatchSize. After the software collects a minimum of NumWarmStartSteps samples, learning occurs at the intervals specified by the LearningFrequency property.

Example: NumWarmStartSteps=20

NumEpoch — Number of times agent learns over data set stored in the experience buffer

1 (default) | positive integer

Number of times an agent learns over the data set stored in the experience buffer, specified as a positive integer. For off-policy agents that support this property (DQN, DDPG, TD3 and SAC), this value defines the number of passes over the data in the replay buffer at each learning iteration.

Example: NumEpoch=2

MaxMiniBatchPerEpoch — Maximum number of mini-batches used for learning during a single epoch

100 (default) | positive integer

Maximum number of mini-batches used for learning during a single epoch, specified as a positive integer.

For off-policy agents that support this property (DQN, DDPG, TD3, and SAC), the actual number of mini-batches used for learning depends on the length of the replay buffer, and MaxMiniBatchPerEpoch specifies the upper bound. This value also specifies the maximum number of gradient steps per learning iteration because the maximum number of gradient steps is equal to the MaxMiniBatchPerEpoch value multiplied by the NumEpoch value.

For off-policy agents that support this property, a high MaxMiniBatchPerEpoch value means that more time is spent on learning than collecting new data. Therefore, you can use this parameter to control the sample efficiency of the learning process.

Example: MaxMiniBatchPerEpoch=200

LearningFrequency — Minimum number of environment interactions between learning iterations

-1 (default) | positive integer

Minimum number of environment interactions between learning iterations, specified as a positive integer or -1. This value defines how many new data samples need to be generated before learning. For DQN, DDPG, TD3, and SAC agents, the default value of -1 means that learning occurs after each episode is finished. Note that for these agents learning can start only after the software collects a minimum of NumWarmStartSteps samples. It then occurs at the intervals specified by the LearningFrequency property.

Example: LearningFrequency=4

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) Agent.

Example: UseDoubleDQN=false

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

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)

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

InfoToSave — Options to save additional agent data

structure (default)

Options to save additional agent data, specified as a structure containing the following fields.

• Optimizer

• PolicyState

• Target

• ExperienceBuffer

You can save an agent object using one of these methods:

• Use the save command.

• Specify saveAgentCriteria and saveAgentValue in an rlTrainingOptions object.

• Specify an appropriate logging function within a FileLogger object.

When you save an agent using any method, the fields in the InfoToSave structure determine whether the corresponding data saves with the agent. For example, if you set the PolicyState field to true, then the policy state saves along with the agent.

You can modify the InfoToSave property only after you create the agent options object.

Example: options.InfoToSave.Optimizer=true

Optimizer — Option to save actor and critic optimizers

false (default) | true

Option to save the actor and critic optimizers, specified as a logical value. If you set the Optimizer field to false, then the actor and critic optimizers (which are hidden properties of the agent and can contain internal states) are not saved along with the agent, therefore saving disk space and memory. However, when the optimizers contains internal states, the state of the saved agent is not identical to the state of the original agent.

Example: true

PolicyState — Option to save state of explorative policy

false (default) | true

Option to save the state of the explorative policy, specified as a logical value. If you set the PolicyState field to false, then the state of the explorative policy (which is a hidden agent property) is not saved along with the agent. In this case, the state of the saved agent is not identical to the state of the original agent.

Example: true

Target — Option to save actor and critic targets

false (default) | true

Option to save the actor and critic targets, specified as a logical value. If you set the Target field to false, then the actor and critic targets (which are hidden agent properties) are not saved along with the agent. In this case, when the targets contain internal states, the state of the saved agent is not identical to the state of the original agent.

Example: true

ExperienceBuffer — Option to save experience buffer

false (default) | true

Option to save the experience buffer, specified as a logical value. If you set the PolicyState field to false, then the content of the experience buffer (which is accessible as an agent property using dot notation) is not saved along with the agent. In this case, the state of the saved agent is not identical to the state of the original agent.

Example: true

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: [1×1 rl.option.EpsilonGreedyExploration]
                 ExperienceBufferLength: 10000
                          MiniBatchSize: 48
                         SequenceLength: 1
                 CriticOptimizerOptions: [1×1 rl.option.rlOptimizerOptions]
                    NumStepsToLookAhead: 1
                      NumWarmStartSteps: 48
                               NumEpoch: 1
                   MaxMiniBatchPerEpoch: 100
                      LearningFrequency: -1
                           UseDoubleDQN: 1
                     TargetSmoothFactor: 1.0000e-03
                  TargetUpdateFrequency: 1
            BatchDataRegularizerOptions: []
    ResetExperienceBufferBeforeTraining: 0
                             InfoToSave: [1×1 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;