"""Warm up learning rate scheduler module."""
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from typing import Union
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import torch
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from torch.optim.lr_scheduler import _LRScheduler
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from funasr.schedulers.abs_scheduler import AbsBatchStepScheduler
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class WarmupLR(_LRScheduler, AbsBatchStepScheduler):
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"""The WarmupLR scheduler
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This scheduler is almost same as NoamLR Scheduler except for following difference:
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NoamLR:
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lr = optimizer.lr * model_size ** -0.5
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* min(step ** -0.5, step * warmup_step ** -1.5)
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WarmupLR:
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lr = optimizer.lr * warmup_step ** 0.5
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* min(step ** -0.5, step * warmup_step ** -1.5)
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Note that the maximum lr equals to optimizer.lr in this scheduler.
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"""
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def __init__(
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self,
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optimizer: torch.optim.Optimizer,
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warmup_steps: Union[int, float] = 25000,
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last_epoch: int = -1,
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):
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self.warmup_steps = warmup_steps
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# __init__() must be invoked before setting field
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# because step() is also invoked in __init__()
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super().__init__(optimizer, last_epoch)
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def __repr__(self):
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return f"{self.__class__.__name__}(warmup_steps={self.warmup_steps})"
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def get_lr(self):
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step_num = self.last_epoch + 1
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return [
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lr * self.warmup_steps**0.5 * min(step_num**-0.5, step_num * self.warmup_steps**-1.5)
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for lr in self.base_lrs
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]
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