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93 lines
3.4 KiB
93 lines
3.4 KiB
from typing import Optional, Union
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import loralib as lora
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import torch
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import torch.nn as nn
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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 - log_probs_base
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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 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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def masked_normalize(tensor: torch.Tensor, mask: torch.Tensor, dim: int = 1, eps: float = 1e-8) -> torch.Tensor:
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tensor = tensor * mask
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mean = masked_mean(tensor, mask, dim=dim)
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mean_centered = tensor - mean
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var = masked_mean(mean_centered**2, mask, dim=dim)
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return mean_centered * var.clamp(min=eps).rsqrt()
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def normalize(tensor: torch.Tensor, dim: int = 0, eps: float = 1e-8) -> torch.Tensor:
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mean = tensor.mean(dim)
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mean_centered = tensor - mean
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var = (mean_centered**2).mean(dim)
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norm = mean_centered * var.clamp(min=eps).rsqrt()
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return norm
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def convert_to_lora(model: nn.Module,
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input_size: int,
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output_size: int,
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lora_rank: int = 16,
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lora_alpha: int = 1,
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lora_dropout: float = 0.,
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fan_in_fan_out: bool = False,
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merge_weights: bool = True):
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if lora_rank > min(input_size, output_size):
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raise ValueError(f"LoRA rank {lora_rank} must be less or equal than {min(input_size, output_size)}")
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for name, module in model.named_modules():
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if isinstance(module, nn.Linear):
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module._modules[name] = lora.Linear(input_size,
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output_size,
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r=lora_rank,
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lora_alpha=lora_alpha,
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lora_dropout=lora_dropout,
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fan_in_fan_out=fan_in_fan_out,
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merge_weights=merge_weights)
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