mirror of https://github.com/hpcaitech/ColossalAI
69 lines
2.3 KiB
Python
69 lines
2.3 KiB
Python
from typing import Optional, Union
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import torch
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import torch.nn.functional as F
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def _compute_approx_kl(log_probs: torch.Tensor,
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log_probs_base: torch.Tensor,
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action_mask: Optional[torch.Tensor] = None) -> torch.Tensor:
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"""
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Compute the approximate KL divergence between two distributions.
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Schulman blog: http://joschu.net/blog/kl-approx.html
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Args:
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log_probs: Log probabilities of the new distribution.
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log_probs_base: Log probabilities of the base distribution.
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action_mask: Mask for actions.
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"""
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log_ratio = log_probs_base - log_probs
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approx_kl = (log_ratio.exp() - 1) - log_ratio
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if action_mask is not None:
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approx_kl = masked_mean(approx_kl, action_mask, dim=1)
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return approx_kl
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approx_kl = approx_kl.mean(dim=1)
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return approx_kl
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def compute_reward(r: Union[torch.Tensor, float],
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kl_coef: float,
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log_probs: torch.Tensor,
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log_probs_base: torch.Tensor,
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action_mask: Optional[torch.Tensor] = None) -> torch.Tensor:
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if kl_coef <= 0.0:
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return r
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kl = _compute_approx_kl(log_probs, log_probs_base, action_mask=action_mask)
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reward = r - kl_coef * kl
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return reward
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def _log_probs_from_logits(logits: torch.Tensor, labels: torch.Tensor) -> torch.Tensor:
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log_probs = F.log_softmax(logits, dim=-1)
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log_probs_labels = log_probs.gather(dim=-1, index=labels.unsqueeze(-1))
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return log_probs_labels.squeeze(-1)
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def calc_action_log_probs(output: torch.Tensor, sequences: torch.LongTensor, num_actions: int) -> torch.Tensor:
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"""Calculate action log probs.
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Args:
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output (torch.Tensor): Output tensor of Actor.forward.
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sequences (torch.LongTensor): Input sequences.
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num_actions (int): Number of actions.
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Returns:
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torch.Tensor: Action log probs.
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"""
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logits = output['logits']
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log_probs = _log_probs_from_logits(logits[:, :-1, :], sequences[:, 1:])
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return log_probs[:, -num_actions:]
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def masked_mean(tensor: torch.Tensor, mask: torch.Tensor, dim: int = 1) -> torch.Tensor:
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tensor = tensor * mask
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tensor = tensor.sum(dim=dim)
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mask_sum = mask.sum(dim=dim)
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mean = tensor / (mask_sum + 1e-8)
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return mean
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