mirror of https://github.com/hpcaitech/ColossalAI
39 lines
1.4 KiB
Python
39 lines
1.4 KiB
Python
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"""
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reward model
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"""
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from typing import Optional
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import torch
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import torch.nn as nn
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from coati.models import BaseModel
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from transformers import PretrainedConfig
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class RewardModel(BaseModel):
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"""
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Reward model class.
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Args:
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pretrained str: huggingface or local model path
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config: PretrainedConfig object
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**kwargs: all other kwargs as in AutoModel.from_pretrained
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"""
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def __init__(self, pretrained: str = None, config: Optional[PretrainedConfig] = None, **kwargs) -> None:
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super().__init__(pretrained=pretrained, config=config, **kwargs)
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self.value_head = nn.Linear(self.last_hidden_state_size, 1)
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self.value_head.weight.data.normal_(mean=0.0, std=1 / (self.last_hidden_state_size + 1))
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def forward(self, input_ids: torch.LongTensor, attention_mask: Optional[torch.Tensor] = None) -> torch.Tensor:
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outputs = self.model(input_ids, attention_mask=attention_mask)
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last_hidden_states = outputs["last_hidden_state"]
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sequence_lengths = torch.max(attention_mask * torch.arange(input_ids.size(1), device=input_ids.device), dim=1)[
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0
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]
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sequence_hidden_states = last_hidden_states[torch.arange(last_hidden_states.size(0)), sequence_lengths].type(
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self.value_head.weight.dtype
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)
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values = self.value_head(sequence_hidden_states).squeeze(-1) # Ensure shape is (B,)
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return values
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