DDPGLoss

class torchrl.objectives.DDPGLoss(*args, **kwargs)

The DDPG Loss class.

Parameters:

• actor_network (TensorDictModule) – a policy operator.

• value_network (TensorDictModule) – a Q value operator.

• loss_function (str) – loss function for the value discrepancy. Can be one of “l1”, “l2” or “smooth_l1”.

• delay_actor (bool, optional) – whether to separate the target actor networks from the actor networks used for data collection. Default is False.

• delay_value (bool, optional) – whether to separate the target value networks from the value networks used for data collection. Default is True.

• separate_losses (bool, optional) – if True, shared parameters between policy and critic will only be trained on the policy loss. Defaults to False, i.e., gradients are propagated to shared parameters for both policy and critic losses.

• reduction (str, optional) – Specifies the reduction to apply to the output: "none" | "mean" | "sum". "none": no reduction will be applied, "mean": the sum of the output will be divided by the number of elements in the output, "sum": the output will be summed. Default: "mean".

Examples

>>> import torch
>>> from torch import nn
>>> from torchrl.data import BoundedTensorSpec
>>> from torchrl.modules.tensordict_module.actors import Actor, ValueOperator
>>> from torchrl.objectives.ddpg import DDPGLoss
>>> from tensordict import TensorDict
>>> n_act, n_obs = 4, 3
>>> spec = BoundedTensorSpec(-torch.ones(n_act), torch.ones(n_act), (n_act,))
>>> actor = Actor(spec=spec, module=nn.Linear(n_obs, n_act))
>>> class ValueClass(nn.Module):
...     def __init__(self):
...         super().__init__()
...         self.linear = nn.Linear(n_obs + n_act, 1)
...     def forward(self, obs, act):
...         return self.linear(torch.cat([obs, act], -1))
>>> module = ValueClass()
>>> value = ValueOperator(
...     module=module,
...     in_keys=["observation", "action"])
>>> loss = DDPGLoss(actor, value)
>>> batch = [2, ]
>>> data = TensorDict({
...        "observation": torch.randn(*batch, n_obs),
...        "action": spec.rand(batch),
...        ("next", "done"): torch.zeros(*batch, 1, dtype=torch.bool),
...        ("next", "terminated"): torch.zeros(*batch, 1, dtype=torch.bool),
...        ("next", "reward"): torch.randn(*batch, 1),
...        ("next", "observation"): torch.randn(*batch, n_obs),
...    }, batch)
>>> loss(data)
TensorDict(
    fields={
        loss_actor: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.float32, is_shared=False),
        loss_value: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.float32, is_shared=False),
        pred_value: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.float32, is_shared=False),
        pred_value_max: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.float32, is_shared=False),
        target_value: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.float32, is_shared=False),
        target_value_max: Tensor(shape=torch.Size([]), device=cpu, dtype=torch.float32, is_shared=False)},
    batch_size=torch.Size([]),
    device=None,
    is_shared=False)

This class is compatible with non-tensordict based modules too and can be used without recurring to any tensordict-related primitive. In this case, the expected keyword arguments are: ["next_reward", "next_done", "next_terminated"] + in_keys of the actor_network and value_network. The return value is a tuple of tensors in the following order: ["loss_actor", "loss_value", "pred_value", "target_value", "pred_value_max", "target_value_max"]

Examples

>>> import torch
>>> from torch import nn
>>> from torchrl.data import BoundedTensorSpec
>>> from torchrl.modules.tensordict_module.actors import Actor, ValueOperator
>>> from torchrl.objectives.ddpg import DDPGLoss
>>> _ = torch.manual_seed(42)
>>> n_act, n_obs = 4, 3
>>> spec = BoundedTensorSpec(-torch.ones(n_act), torch.ones(n_act), (n_act,))
>>> actor = Actor(spec=spec, module=nn.Linear(n_obs, n_act))
>>> class ValueClass(nn.Module):
...     def __init__(self):
...         super().__init__()
...         self.linear = nn.Linear(n_obs + n_act, 1)
...     def forward(self, obs, act):
...         return self.linear(torch.cat([obs, act], -1))
>>> module = ValueClass()
>>> value = ValueOperator(
...     module=module,
...     in_keys=["observation", "action"])
>>> loss = DDPGLoss(actor, value)
>>> loss_actor, loss_value, pred_value, target_value, pred_value_max, target_value_max = loss(
...     observation=torch.randn(n_obs),
...     action=spec.rand(),
...     next_done=torch.zeros(1, dtype=torch.bool),
...     next_terminated=torch.zeros(1, dtype=torch.bool),
...     next_observation=torch.randn(n_obs),
...     next_reward=torch.randn(1))
>>> loss_actor.backward()

The output keys can also be filtered using the DDPGLoss.select_out_keys() method.

Examples

>>> loss.select_out_keys('loss_actor', 'loss_value')
>>> loss_actor, loss_value = loss(
...     observation=torch.randn(n_obs),
...     action=spec.rand(),
...     next_done=torch.zeros(1, dtype=torch.bool),
...     next_terminated=torch.zeros(1, dtype=torch.bool),
...     next_observation=torch.randn(n_obs),
...     next_reward=torch.randn(1))
>>> loss_actor.backward()

forward(tensordict: TensorDictBase) → TensorDict

Computes the DDPG losses given a tensordict sampled from the replay buffer.

This function will also write a “td_error” key that can be used by prioritized replay buffers to assign

a priority to items in the tensordict.

Parameters:

tensordict (TensorDictBase) – a tensordict with keys [“done”, “terminated”, “reward”] and the in_keys of the actor and value networks.

Returns:

a tuple of 2 tensors containing the DDPG loss.

make_value_estimator(value_type: Optional[ValueEstimators] = None, **hyperparams)

Value-function constructor.

If the non-default value function is wanted, it must be built using this method.

Parameters:

• value_type (ValueEstimators) – A ValueEstimators enum type indicating the value function to use. If none is provided, the default stored in the default_value_estimator attribute will be used. The resulting value estimator class will be registered in self.value_type, allowing future refinements.

• **hyperparams – hyperparameters to use for the value function. If not provided, the value indicated by default_value_kwargs() will be used.

Examples

>>> from torchrl.objectives import DQNLoss
>>> # initialize the DQN loss
>>> actor = torch.nn.Linear(3, 4)
>>> dqn_loss = DQNLoss(actor, action_space="one-hot")
>>> # updating the parameters of the default value estimator
>>> dqn_loss.make_value_estimator(gamma=0.9)
>>> dqn_loss.make_value_estimator(
...     ValueEstimators.TD1,
...     gamma=0.9)
>>> # if we want to change the gamma value
>>> dqn_loss.make_value_estimator(dqn_loss.value_type, gamma=0.9)