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| import math
import torch from torch.optim import Optimizer from torch.optim.lr_scheduler import LambdaLR
def get_cosine_schedule_with_warmup( optimizer: Optimizer, num_warmup_steps: int, num_training_steps: int, num_cycles: float = 0.5, last_epoch: int = -1, ): """ Create a schedule with a learning rate that decreases following the values of the cosine function between the initial lr set in the optimizer to 0, after a warmup period during which it increases linearly between 0 and the initial lr set in the optimizer.
Args: optimizer (:class:`~torch.optim.Optimizer`): The optimizer for which to schedule the learning rate. num_warmup_steps (:obj:`int`): The number of steps for the warmup phase. num_training_steps (:obj:`int`): The total number of training steps. num_cycles (:obj:`float`, `optional`, defaults to 0.5): The number of waves in the cosine schedule (the defaults is to just decrease from the max value to 0 following a half-cosine). last_epoch (:obj:`int`, `optional`, defaults to -1): The index of the last epoch when resuming training.
Return: :obj:`torch.optim.lr_scheduler.LambdaLR` with the appropriate schedule. """ def lr_lambda(current_step): if current_step < num_warmup_steps: return float(current_step) / float(max(1, num_warmup_steps)) progress = float(current_step - num_warmup_steps) / float( max(1, num_training_steps - num_warmup_steps) ) return max( 0.0, 0.5 * (1.0 + math.cos(math.pi * float(num_cycles) * 2.0 * progress)) )
return LambdaLR(optimizer, lr_lambda, last_epoch)
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