A2C

.gitignore

@@ -171,4 +171,5 @@ pytest_*
 mlruns
 mlartifacts
 examples/models
-session_*
+session_*
+bin/

README.md

@@ -82,8 +82,8 @@ The algorithms sheeped by sheeprl out-of-the-box are:
 
 | Algorithm                 | Coupled            | Decoupled          | Recurrent          | Vector obs         | Pixel obs          | Status             |
 | ------------------------- | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ |
-| A2C                       | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :construction:     |
-| A3C                       | :heavy_check_mark: | :x:                | :x:                | :heavy_check_mark: | :heavy_check_mark: | :construction:     |
+| A2C                       | :heavy_check_mark: | :x:                | :x:                | :heavy_check_mark: | :x:                | :heavy_check_mark: |
+| A3C                       | :heavy_check_mark: | :x:                | :x:                | :heavy_check_mark: | :x:                | :construction:     |
 | PPO                       | :heavy_check_mark: | :heavy_check_mark: | :x:                | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | PPO Recurrent             | :heavy_check_mark: | :x:                | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | SAC                       | :heavy_check_mark: | :heavy_check_mark: | :x:                | :heavy_check_mark: | :x:                | :heavy_check_mark: |

howto/register_new_algorithm.md

@@ -138,6 +138,7 @@ def sota_main(fabric: Fabric, cfg: Dict[str, Any]):
         fabric._loggers = [logger]
         fabric.logger.log_hyperparams(cfg)
     log_dir = get_log_dir(fabric, cfg.root_dir, cfg.run_name)
+    fabric.print(f"Log dir: {log_dir}")
 
     # Environment setup
     vectorized_env = gym.vector.SyncVectorEnv if cfg.env.sync_env else gym.vector.AsyncVectorEnv

sheeprl/__init__.py

@@ -15,6 +15,7 @@
 import numpy as np
 
 # fmt: off
+from sheeprl.algos.a2c import a2c  # noqa: F401
 from sheeprl.algos.dreamer_v1 import dreamer_v1  # noqa: F401
 from sheeprl.algos.dreamer_v2 import dreamer_v2  # noqa: F401
 from sheeprl.algos.dreamer_v3 import dreamer_v3  # noqa: F401

sheeprl/algos/a2c/README.md

@@ -0,0 +1,35 @@
+# A2C algorithm
+Advantage-Actor-Critic (A2C) is an on-policy algorithm that uses the standard policy gradient algorithm, scaled by the advantages, to update the policy.
+
+From the interaction with the environment, it collects trajectories of *observations*, *actions*, *rewards*, *values*, *logprobs* and *dones*. These trajectories are stored in a buffer, and used to train the policy and value networks.
+
+Indeed, the training loop consists in sampling a batch of trajectories from the buffer, and computing the *policy loss*, *value loss* and *entropy loss*, while accumulating the gradients over the trajectories collected during the interaction with the environment. By deafult it will sum the gradients over multiple batches, averaging them across all replicas on the last batch seen.
+
+From the rewards, *returns* and *advantages* are estimated. The *returns*, together with the values stored in the buffer and the values from the updated critic, are used to compute the *value loss*. 
+
+```python
+def value_loss(
+    values: Tensor,
+    returns: Tensor,
+    clip_coef: float,
+    clip_vloss: bool,
+) -> Tensor:
+    return mse_loss(values, returns)
+```
+
+Advantages and logprobs are used to compute the *policy loss*, using also the logprobs from the updated model.
+
+```python
+def policy_loss(logprobs: Tensor, advantages: Tensor) -> Tensor:
+    pg_loss = -logprobs * advantages.detach()
+    reduction = reduction.lower()
+    if reduction == "none":
+        return pg_loss
+    elif reduction == "mean":
+        return pg_loss.mean()
+    elif reduction == "sum":
+        return pg_loss.sum()
+    else:
+        raise ValueError(f"Unrecognized reduction: {reduction}")
+```
+