rlContinuousDeterministicActor

R2026b

Deterministic actor with a continuous action space for reinforcement learning agents

Since R2022a

Description

This object implements a function approximator to be used as a deterministic actor within a reinforcement learning agent with a continuous action space. A continuous deterministic actor takes an environment observation as input and returns as output an action that is a parameterized deterministic function of the observation, thereby implementing a parameterized deterministic policy. After you create an rlContinuousDeterministicActor object, use it to create a suitable agent, such as rlDDPGAgent. For more information on creating actors and critics, see Create Actors, Critics, and Policy Objects.

Creation

Syntax

actor = rlContinuousDeterministicActor(net,observationInfo,actionInfo)

actor = rlContinuousDeterministicActor({basisFcn,W0},observationInfo,actionInfo)

actor = rlContinuousDeterministicActor(___,Name=Value)

Description

actor = rlContinuousDeterministicActor(net,observationInfo,actionInfo) creates a continuous deterministic actor object using the deep neural network net as underlying approximation model. For this actor, actionInfo must specify a continuous action space. The network input layers are automatically associated with the environment observation channels according to the dimension specifications in observationInfo. The network must have a single output layer with the same data type and dimensions as the action specified in actionInfo.

actor = rlContinuousDeterministicActor({basisFcn,W0},observationInfo,actionInfo) creates a continuous deterministic actor object using a custom basis function as underlying approximation model. The first input argument is a two-element cell array whose first element is the handle basisFcn to a custom basis function and whose second element is the initial weight vector W0. This function sets the ObservationInfo and ActionInfo properties of actor to the observationInfo and actionInfo input arguments, respectively.

actor = rlContinuousDeterministicActor(___,Name=Value) specifies names of the observation input layers (for network-based approximators) or sets the UseDevice property using one or more name-value arguments. Specifying the input layer names allows you explicitly associate the layers of your network approximator with specific environment channels. For all types of approximators, you can specify the device where computations for actor are executed, for example, UseDevice="gpu".

Input Arguments

net — Deep neural network

array of Layer objects | layerGraph object | DAGNetwork object | SeriesNetwork object | dlNetwork object (preferred)

Deep neural network used as the underlying approximation model within the actor, specified as follows:

• Array of Layer objects

• layerGraph object

• DAGNetwork object

• SeriesNetwork object

• dlnetwork object

Note

Among the different network representation options, dlnetwork is preferred, since it has built-in validation checks and supports automatic differentiation. If you pass another network object as an input argument, it is internally converted to a dlnetwork object. However, best practice is to convert other representations to dlnetwork explicitly before using them to create a critic or an actor for a reinforcement learning agent. You can do so using dlnet=dlnetwork(net), where net is any Deep Learning Toolbox™ neural network object. The resulting dlnet is the dlnetwork object that you use for your critic or actor. This practice allows a greater level of insight and control for cases in which the conversion is not straightforward and might require additional specifications.

The network must have as many input layers as the number of environment observation channels (with each input layer receiving input from an observation channel), and a single output layer returning the action.

rlContinuousDeterministicActor objects support recurrent deep neural networks. For an example, see Create Deterministic Actor from Recurrent Neural Network.

The learnable parameters of the actor are the weights of the deep neural network. For a list of deep neural network layers, see List of Deep Learning Layers. For more information on creating deep neural networks for reinforcement learning, see Create Actors, Critics, and Policy Objects.

Example: net = dlnetwork([featureInputLayer(2) fullyConnectedLayer(10) reluLayer fullyConnectedLayer(1)]) creates the dlnetwork object net.

basisFcn — Custom basis function

function handle

Custom basis function, specified as a function handle to a user-defined MATLAB function. The user defined function can either be an anonymous function or a function on the MATLAB path. The action to be taken based on the current observation, which is the output of the actor, is the vector a = W'*B, where W is a weight matrix containing the learnable parameters and B is the column vector returned by the custom basis function.

Your basis function must have the following signature.

B = myBasisFunction(obs1,obs2, ...,obsN)

Here, obs1 to obsN are inputs in the same order and with the same data type and initial dimensions as the environment observation channels defined in observationInfo. Since the training algorithm normally executes on batches of observations and actions at the same time, these inputs must also have an additional (last) batch dimension.

Example: @(obs1,obs2,obs3) [obs3(2,1,:)*obs1(1,1,:)^2; abs(obs2(5,1,:)+obs3(1,1:))]

W0 — Initial value of basis function weights

matrix

Initial value of the basis function weights W, specified as a matrix having as many rows as the length of the vector returned by the basis function and as many columns as the dimension of the action space.

Example: W0 = rand(2,1)

observationInfo — Observation specifications

rlFiniteSetSpec object | rlNumericSpec object | array

Observation specifications, specified as an rlFiniteSetSpec or rlNumericSpec object or an array containing any combination of such objects. Each element in the array defines the properties of an environment observation channel, such as its dimensions, data type, and name.

This argument sets the ObservationInfo property.

Example: observationInfo=[rlNumericSpec([2 1]) rlFiniteSetSpec([-1 1])]

actionInfo — Observation specifications

rlNumericSpec object

Action specifications, specified as an rlNumericSpec object. This object defines the properties of the environment action channel, such as its dimensions, data type, and name.

This argument sets the ActionInfo property.

Note

For this approximator object, only one action channel is allowed.

Example: actionInfo=rlNumericSpec([1 2])

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: UseDevice="gpu"

ObservationInputNames — Network input layers names corresponding to the environment observation channels

string array | cell array of strings | cell array of character vectors

Network input layers names corresponding to the environment observation channels, specified as a string array or a cell array of strings or character vectors. The function assigns, in sequential order, each environment observation channel specified in observationInfo to each layer whose name is specified in the array assigned to this argument. Therefore, the specified network input layers, ordered as indicated in this argument, must have the same data type and dimensions as the observation channels, as ordered in observationInfo.

This name-value argument is supported only when the approximation model is a deep neural network.

Example: ObservationInputNames={"obsInLyr1_airspeed","obsInLyr2_altitude"}

UseDevice — Computation device used for training and simulation

"cpu" (default) | "gpu"

Computation device used for training and simulation, specified as "cpu" or "gpu". By default, the approximator uses "cpu" for training and simulation. This argument sets the UseDevice property.

Example: UseDevice="gpu"

Properties

ObservationInfo — Observation specifications

Read-only: rlFiniteSetSpec object | rlNumericSpec object | array

This property is read-only.

Observation specifications, specified as an rlFiniteSetSpec or rlNumericSpec object or an array containing any combination of such objects. Each element in the array defines the properties of an environment observation channel, such as its dimensions, data type, and name.

When you create the approximator object, the constructor function sets the ObservationInfo property to the input argument observationInfo.

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

ActionInfo — Action specifications

Read-only: rlNumericSpec object

This property is read-only.

Action specifications, specified as an rlNumericSpec object. This object defines the properties of the environment action channel, such as its dimensions, data type, and name.

Note

For this approximator object, only one action channel is allowed.

When you create the approximator object, the constructor function sets the ActionInfo property to the input argument actionInfo.

You can extract ActionInfo from an existing environment, approximator object, or agent using getActionInfo. You can also construct the specification manually using rlNumericSpec.

Normalization — Normalization method

"none" (default) | string array

Normalization method, returned as an array in which each element (one for each input channel defined in the observationInfo and actionInfo properties, in that order) is one of the following values:

• "none" — Do not normalize the input.

• "rescale-zero-one" — Normalize the input by rescaling it to the interval between 0 and 1. The normalized input Y is (U–Min)./(UpperLimit–LowerLimit), where U is the nonnormalized input. Note that nonnormalized input values lower than LowerLimit result in normalized values lower than 0. Similarly, nonnormalized input values higher than UpperLimit result in normalized values higher than 1. Here, UpperLimit and LowerLimit are the corresponding properties defined in the specification object of the input channel.

• "rescale-symmetric" — Normalize the input by rescaling it to the interval between –1 and 1. The normalized input Y is 2(U–LowerLimit)./(UpperLimit–LowerLimit) – 1, where U is the nonnormalized input. Note that nonnormalized input values lower than LowerLimit result in normalized values lower than –1. Similarly, nonnormalized input values higher than UpperLimit result in normalized values higher than 1. Here, UpperLimit and LowerLimit are the corresponding properties defined in the specification object of the input channel.

Note

When you specify the Normalization property of rlAgentInitializationOptions, normalization is applied only to the approximator input channels corresponding to rlNumericSpec specification objects in which both the UpperLimit and LowerLimit properties are defined. After you create the agent, you can use the setNormalizer function to assign normalizers that use any normalization method. For more information on normalizer objects, see rlNormalizer.

Example: myActor.Normalization = "rescale-symmetric" sets to "rescale-symmetric" the Normalization property of the function approximator myActor.

UseDevice — Computation device used for training and simulation

"cpu" (default) | "gpu"

Computation device used to perform operations such as gradient computation, parameter update and prediction during training and simulation, specified as either "cpu" or "gpu".

The "gpu" option requires both Parallel Computing Toolbox™ software and a CUDA^® enabled NVIDIA^® GPU. For more information on supported GPUs see GPU Computing Requirements (Parallel Computing Toolbox).

You can use gpuDevice (Parallel Computing Toolbox) to query or select a local GPU device to be used with MATLAB^®.

Note

Training or simulating an agent on a GPU involves device-specific numerical round-off errors. Because of these errors, you can get different results on a GPU and on a CPU for the same operation.

To scale up the number of environment simulations by using parallel processing over multiple cores, you do not need to use this property. Instead, set the UseParallel training option to "on" or "auto". For more information about training using multicore processors and GPUs for training, see Train Agents Using Parallel Computing and GPUs.

Example: myCritic.UseDevice = "gpu" sets to "gpu" the UseDevice property of the function approximator myCritic.

Learnables — Learnable parameters of approximator object

cell array of dlarray objects

Learnable parameters of the approximator object, specified as a cell array of dlarray objects. This property contains the learnable parameters of the approximation model used by the approximator object.

Example: myActor.Learnables = {dlarray(rand(256,4)),dlarray(rand(256,1))} sets the learnable parameters of the function approximator myActor.

State — State of approximator object

cell array of dlarray objects

State of the approximator object, specified as a cell array of dlarray objects. For dlnetwork-based models, this property contains the Value column of the State property table of the dlnetwork model. The elements of the cell array are the state of the recurrent neural network used in the approximator (if any), as well as the state for the batch normalization layer (if used).

For model types that are not based on a dlnetwork object, this property is an empty cell array, since these model types do not support states.

Example: myCritic.State={dlarray(rand(256,1)),dlarray(rand(256,1))} sets the state of the function approximator myCritic.

Object Functions

rlDDPGAgent	Deep deterministic policy gradient (DDPG) reinforcement learning agent
rlTD3Agent	Twin-delayed deep deterministic (TD3) policy gradient reinforcement learning agent
getAction	Obtain action from agent, actor, or policy object given environment observations
evaluate	Evaluate function approximator object given observation (or observation-action) input data
gradient	(Not recommended) Evaluate gradient of function approximator object given observation and action input data
accelerate	(Not recommended) Option to accelerate computation of gradient for approximator object based on neural network
getLearnableParameters	Obtain learnable parameter values from agent, function approximator, or policy object
setLearnableParameters	Set learnable parameter values of agent, function approximator, or policy object
setModel	Set approximation model in function approximator object
getModel	Get approximation model from function approximator object

Examples

Create Continuous Deterministic Actor from Deep Neural Network

Create an observation specification object (or alternatively use the getObservationInfo function to extract the specification object from an environment). For this example, define the observation space as a continuous four-dimensional space, so that there is a single observation channel that carries a column vector containing four doubles.

obsInfo = rlNumericSpec([4 1]);

Create an action specification object (or alternatively use the getActionInfo function to extract the specification object from an environment). For this example, define the action space as a continuous two-dimensional space, so that the action channel carries a column vector containing two doubles.

actInfo = rlNumericSpec([2 1]);

A continuous deterministic actor implements a parameterized deterministic policy for a continuous action space. This actor takes the current observation as input and returns as output an action that is a deterministic function of the observation.

To model the parameterized policy within the actor, use a neural network with one input layer (which receives the content of the environment observation channel, as specified by obsInfo) and one output layer (which returns the action to the environment action channel, as specified by actInfo).

Define the network as an array of layer objects, and get the dimension of the observation and action spaces from the environment specification objects.

net = [ 
    featureInputLayer(obsInfo.Dimension(1))
    fullyConnectedLayer(32)
    reluLayer
    fullyConnectedLayer(actInfo.Dimension(1))
    ];

Convert the network to a dlnetwork object and display the number of learnable parameters.

net = dlnetwork(net);
summary(net)

   Initialized: true

   Number of learnables: 226

   Inputs:
      1   'input'   4 features

Create the actor object with rlContinuousDeterministicActor, using the network and the observation and action specification objects as input arguments. The network input layer is automatically associated with the environment observation channel according to the dimension specifications in obsInfo.

actor = rlContinuousDeterministicActor( ...
    net, ...
    obsInfo, ...
    actInfo)

actor = 
  rlContinuousDeterministicActor with properties:

    ObservationInfo: [1×1 rl.util.rlNumericSpec]
         ActionInfo: [1×1 rl.util.rlNumericSpec]
      Normalization: "none"
          UseDevice: "cpu"
         Learnables: {4×1 cell}
              State: {0×1 cell}

To check your actor, use the getAction function to return the action from a random observation, using the current network weights.

act = getAction(actor, ...
    {rand(obsInfo.Dimension)}); 
act{1}

ans = 2×1 single column vector

   -0.0684
   -0.2538

You can now use the actor (along with a critic) to create an agent for the environment described by the given specification objects. Examples of agents that can work with continuous action and observation spaces, and use a continuous deterministic actor, are rlDDPGAgent and rlTD3Agent.

For more information on creating approximator objects such as actors and critics, see Create Actors, Critics, and Policy Objects.

Create Continuous Deterministic Actor Specifying Network Input Layer Name

Create an observation specification object (or alternatively use the getObservationInfo function to extract the specification object from an environment). For this example, define the observation space as a continuous four-dimensional space, so that there is a single observation channel that carries a column vector containing four doubles.

obsInfo = rlNumericSpec([4 1]);

Create an action specification object (or alternatively use the getActionInfo function to extract the specification object from an environment). For this example, define the action space as a continuous two-dimensional space, so that the action channel carries a column vector containing two doubles.

actInfo = rlNumericSpec([2 1]);

A continuous deterministic actor implements a parameterized deterministic policy for a continuous action space. This actor takes the current observation as input and returns an action as output.

To model the parameterized policy within the actor, use a neural network with one input layer (which receives the content of the environment observation channel, as specified by obsInfo) and one output layer (which returns the action to the environment action channel, as specified by actInfo).

Define the network as an array of layer objects, and get the dimension of the observation and action spaces from the environment specification objects. Name the network input layer obsInLyr so you can later explicitly associate it to the observation input channel.

net = [
    featureInputLayer(obsInfo.Dimension(1),Name="obsInLyr")
    fullyConnectedLayer(16)
    reluLayer
    fullyConnectedLayer(actInfo.Dimension(1))
    ];

Convert the network to a dlnetwork object, and display the number of learnable parameters.

net = dlnetwork(net);
summary(net)

   Initialized: true

   Number of learnables: 114

   Inputs:
      1   'obsInLyr'   4 features

Create the actor object with rlContinuousDeterministicActor, using the network, the observation and action specification objects, and the name of the network input layer to be associated with the environment observation channel.

actor = rlContinuousDeterministicActor(net, ...
            obsInfo,actInfo, ...
            Observation="obsInLyr")

actor = 
  rlContinuousDeterministicActor with properties:

    ObservationInfo: [1×1 rl.util.rlNumericSpec]
         ActionInfo: [1×1 rl.util.rlNumericSpec]
      Normalization: "none"
          UseDevice: "cpu"
         Learnables: {4×1 cell}
              State: {0×1 cell}

To check your actor, use the getAction function to return the action from a batch of 10 random observations, using the current network weights.

robs = rand([obsInfo.Dimension 10]);
act = getAction(actor,{robs});

Display the fifth element of the action batch.

act{1}(5)

ans = single

0.4152

You can now use the actor (along with a critic) to create an agent for the environment described by the given specification objects. Examples of agents that can work with continuous action and observation spaces, and use a continuous deterministic actor, are rlDDPGAgent and rlTD3Agent.

For more information on creating approximator objects such as actors and critics, see Create Actors, Critics, and Policy Objects.

Create Continuous Deterministic Actor from Custom Basis Function

Create an observation specification object (or alternatively use the getObservationInfo function to extract the specification object from an environment). For this example, define the observation space as consisting of two environment channels, the first containing a two-by-two continuous matrix and the second containing a scalar that can be only 0 or 1.

obsInfo = [rlNumericSpec([2 2]) 
           rlFiniteSetSpec([0 1])];

Create a continuous action space specification object (or alternatively use the getActionInfo function to extract the specification object from an environment). For this example, define the action space as a continuous three-dimensional space, so that the environment action channel carries a column vector containing three doubles.

actInfo = rlNumericSpec([3 1]);

A continuous deterministic actor implements a parameterized deterministic policy for a continuous action space. This actor takes a batch of observations as inputs and returns a corresponding batch of actions that are a deterministic function of the observations.

To model the parameterized policy within the actor, use a custom basis function. The function must have two input arguments, each receiving the content of an environment observation channel, as specified by obsInfo.

Note that using local functions to implement a custom basis function is not recommended if you want to save an agent and load it later. This is because local functions are available only in the file in which they are defined, and when you load an agent in the workspace the function is no longer available to the agent. Additionally, local functions are not supported for code generation.

Write a simple custom basis function as a string (alternatively, write your own custom basis function in a file).

str =  "function out = myBasisFcn(obsA,obsB)" + newline + ... 
    " out = [obsA(1,1,:).*obsB(1,1,:).^2;" + newline + ...
    "        obsA(2,1,:).*obsB(1,1,:).^2;" + newline + ...
    "        obsA(1,2,:).^2+obsB(1,1,:);" + newline + ...
    "        obsA(2,2,:).^2-obsB(1,1,:)];" + newline + ...
    "end"

str = 
    "function out = myBasisFcn(obsA,obsB)
      out = [obsA(1,1,:).*obsB(1,1,:).^2;
             obsA(2,1,:).*obsB(1,1,:).^2;
             obsA(1,2,:).^2+obsB(1,1,:);
             obsA(2,2,:).^2-obsB(1,1,:)];
     end"

Here, the first two dimensions of the observations are the ones defined in the obsInfo elements, while the third dimension is the batch dimension. Since the training algorithm normally executes on batches of observations and actions at the same time, you have to keep the batch dimension into account when writing your custom basis function. For each element of the batch dimension, the function returns a vector of four elements

Write the string to the myBasisFcn.m file and check that the file exists.

fid=fopen("myBasisFcn.m","w");
fwrite(fid,str,"char");
fclose(fid);
exist("myBasisFcn.m","file")

ans = 
2

The output of the actor is the vector W'*myBasisFcn(obsA,obsB), which is the action taken as a result of the given observation. The weight matrix W contains the learnable parameters and must have as many rows as the length of the basis function output and as many columns as the dimension of the action space.

Define an initial parameter matrix.

W0 = rand(4,3);

Create the actor. The first argument is a two-element cell containing both the handle to the custom function and the initial weight matrix. The second and third arguments are, respectively, the observation and action specification objects.

actor = rlContinuousDeterministicActor({@myBasisFcn,W0},obsInfo,actInfo)

actor = 
  rlContinuousDeterministicActor with properties:

    ObservationInfo: [2×1 rl.util.RLDataSpec]
         ActionInfo: [1×1 rl.util.rlNumericSpec]
      Normalization: ["none"    "none"]
          UseDevice: "cpu"
         Learnables: {[3×4 dlarray]}
              State: {}

To check your actor, use the getAction function to return the action from a given observation, using the current parameter matrix.

a = getAction(actor,{rand(2,2),0})

a = 1×1 cell array
    {3×1 double}

a{1}

ans = 3×1

    0.5097
    0.4915
    0.5625

a = getAction(actor,{rand(2,2),-1});
a{1}

ans = 3×1

    2.1162
    0.8687
    2.2511

Note that the actor does not enforce the set constraint for the discrete set elements.

Return a batch of actions resulting from a batch of 5 observations.

obs1 = rand([obsInfo(1).Dimension 5]);
obs2 = rand([obsInfo(2).Dimension 5]);
act = getAction(actor,{obs1,obs2});

Display the fourth element in the batch.

act{1}(:,4)

ans = 3×1

    0.1812
    0.0628
    0.2245

You can now use the actor (along with a critic) to create an agent for the environment described by the given specification objects. Examples of agents that can work with a mixed observation space, a continuous action space, and use a continuous deterministic actor, are rlDDPGAgent and rlTD3Agent.

For more information on creating approximator objects such as actors and critics, see Create Actors, Critics, and Policy Objects.

Create Deterministic Actor from Recurrent Neural Network

Create observation and action information. You can also obtain these specifications from an environment. For this example, define the observation space as a continuous four-dimensional space, so that a single observation channel carries a column vector containing four doubles, and the action space as a continuous two-dimensional space, so that the action channel carries a column vector containing two doubles.

obsInfo = rlNumericSpec([4 1]);
actInfo = rlNumericSpec([2 1]);

A continuous deterministic actor implements a parameterized deterministic policy for a continuous action space. This actor takes the current observation as input and returns as output an action that is a deterministic function of the observation.

To model the parameterized policy within the actor, use a neural network with one input layer (which receives the content of the environment observation channel, as specified by obsInfo) and one output layer (which returns the action to the environment action channel, as specified by actInfo).

Define the network as an array of layer objects, and get the dimension of the observation and action spaces from the environment specification objects. Because this network is recurrent, use a sequenceInputLayer as the input layer and include at least one lstmLayer.

net = [
    sequenceInputLayer(obsInfo.Dimension(1))
    fullyConnectedLayer(10)
    reluLayer
    lstmLayer(8,OutputMode="sequence")
    fullyConnectedLayer(20)
    fullyConnectedLayer(actInfo.Dimension(1))
    tanhLayer
    ];

Convert the network to a dlnetwork object and display the number of learnable parameters.

net = dlnetwork(net);
summary(net)

   Initialized: true

   Number of learnables: 880

   Inputs:
      1   'sequenceinput'   Sequence input with 4 channels

Create a deterministic actor representation for the network.

actor = rlContinuousDeterministicActor( ...
    net, ...
    obsInfo, ...
    actInfo);

To check your actor, use the getAction function to return the action from a random observation, given the current network weights.

a = getAction(actor, ...
    {rand(obsInfo.Dimension)}); 
a{1}

ans = 2×1 single column vector

   -0.0742
    0.0158

You can use dot notation to extract and set the current state of the recurrent neural network in the actor.

actor.State

ans = 2×1 cell array
    {8×1 dlarray}
    {8×1 dlarray}

actor.State = {
      dlarray(-0.1*rand(8,1))
      dlarray(0.1*rand(8,1)) 
      };

To evaluate the actor using sequential observations, use the sequence length (time) dimension. For example, obtain actions for a batch of 5 independent sequences each one consisting of 9 sequential observations.

[action,state] = getAction(actor, ...
    {rand([obsInfo.Dimension 5 9])});

Display the action corresponding to the seventh element of the observation sequence in the fourth sequence.

action = action{1};
action(1,1,4,7)

ans = single

-0.2408

Display the updated state of the recurrent neural network.

state

state = 2×1 cell array
    {8×5 single}
    {8×5 single}

You can now use the actor (along with a critic) to create an agent for the environment described by the given specification objects. Examples of agents that can work with continuous action and observation spaces, and use a continuous deterministic actor, are rlDDPGAgent and rlTD3Agent.

For more information on input and output format for recurrent neural networks, see the Algorithms section of lstmLayer. For more information on creating approximator objects such as actors and critics, see Create Actors, Critics, and Policy Objects.

Extended Capabilities

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Version History

Introduced in R2022a