Source code for ray.rllib.evaluation.postprocessing

import numpy as np
import scipy.signal
from ray.rllib.policy.sample_batch import SampleBatch
from ray.rllib.utils.annotations import DeveloperAPI

def discount(x, gamma):
    return scipy.signal.lfilter([1], [1, -gamma], x[::-1], axis=0)[::-1]

class Postprocessing:
    """Constant definitions for postprocessing."""

    ADVANTAGES = "advantages"
    VALUE_TARGETS = "value_targets"

[docs]@DeveloperAPI def compute_advantages(rollout, last_r, gamma=0.9, lambda_=1.0, use_gae=True, use_critic=True): """ Given a rollout, compute its value targets and the advantage. Args: rollout (SampleBatch): SampleBatch of a single trajectory last_r (float): Value estimation for last observation gamma (float): Discount factor. lambda_ (float): Parameter for GAE use_gae (bool): Using Generalized Advantage Estimation use_critic (bool): Whether to use critic (value estimates). Setting this to False will use 0 as baseline. Returns: SampleBatch (SampleBatch): Object with experience from rollout and processed rewards. """ traj = {} trajsize = len(rollout[SampleBatch.ACTIONS]) for key in rollout: traj[key] = np.stack(rollout[key]) assert SampleBatch.VF_PREDS in rollout or not use_critic, \ "use_critic=True but values not found" assert use_critic or not use_gae, \ "Can't use gae without using a value function" if use_gae: vpred_t = np.concatenate( [rollout[SampleBatch.VF_PREDS], np.array([last_r])]) delta_t = ( traj[SampleBatch.REWARDS] + gamma * vpred_t[1:] - vpred_t[:-1]) # This formula for the advantage comes from: # "Generalized Advantage Estimation": traj[Postprocessing.ADVANTAGES] = discount(delta_t, gamma * lambda_) traj[Postprocessing.VALUE_TARGETS] = ( traj[Postprocessing.ADVANTAGES] + traj[SampleBatch.VF_PREDS]).copy().astype(np.float32) else: rewards_plus_v = np.concatenate( [rollout[SampleBatch.REWARDS], np.array([last_r])]) discounted_returns = discount(rewards_plus_v, gamma)[:-1].copy().astype(np.float32) if use_critic: traj[Postprocessing. ADVANTAGES] = discounted_returns - rollout[SampleBatch. VF_PREDS] traj[Postprocessing.VALUE_TARGETS] = discounted_returns else: traj[Postprocessing.ADVANTAGES] = discounted_returns traj[Postprocessing.VALUE_TARGETS] = np.zeros_like( traj[Postprocessing.ADVANTAGES]) traj[Postprocessing.ADVANTAGES] = traj[ Postprocessing.ADVANTAGES].copy().astype(np.float32) assert all(val.shape[0] == trajsize for val in traj.values()), \ "Rollout stacked incorrectly!" return SampleBatch(traj)