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104 lines
3.5 KiB
104 lines
3.5 KiB
import logging
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import math
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import numpy as np
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import torch
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from .scheduler import Scheduler
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logger = logging.getLogger(__name__)
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class CosineLRScheduler(Scheduler):
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"""
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Cosine decay with restarts.
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This is described in the paper https://arxiv.org/abs/1608.03983.
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Inspiration from
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https://github.com/allenai/allennlp/blob/master/allennlp/training/learning_rate_schedulers/cosine.py
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"""
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def __init__(self,
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optimizer: torch.optim.Optimizer,
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t_initial: int,
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t_mul: float = 1.,
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lr_min: float = 0.,
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decay_rate: float = 1.,
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warmup_t=0,
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warmup_lr_init=0,
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warmup_prefix=False,
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cycle_limit=0,
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t_in_epochs=True,
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initialize=True) -> None:
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super().__init__(optimizer, param_group_field="lr", initialize=initialize)
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assert t_initial > 0
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assert lr_min >= 0
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if t_initial == 1 and t_mul == 1 and decay_rate == 1:
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logger.warning("Cosine annealing scheduler will have no effect on the learning "
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"rate since t_initial = t_mul = eta_mul = 1.")
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self.t_initial = t_initial
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self.t_mul = t_mul
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self.lr_min = lr_min
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self.decay_rate = decay_rate
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self.cycle_limit = cycle_limit
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self.warmup_t = warmup_t
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self.warmup_lr_init = warmup_lr_init
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self.warmup_prefix = warmup_prefix
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self.t_in_epochs = t_in_epochs
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if self.warmup_t:
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self.warmup_steps = [(v - warmup_lr_init) / self.warmup_t for v in self.base_values]
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super().update_groups(self.warmup_lr_init)
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else:
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self.warmup_steps = [1 for _ in self.base_values]
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def _get_lr(self, t):
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if t < self.warmup_t:
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lrs = [self.warmup_lr_init + t * s for s in self.warmup_steps]
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else:
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if self.warmup_prefix:
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t = t - self.warmup_t
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if self.t_mul != 1:
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i = math.floor(math.log(1 - t / self.t_initial * (1 - self.t_mul), self.t_mul))
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t_i = self.t_mul ** i * self.t_initial
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t_curr = t - (1 - self.t_mul ** i) / (1 - self.t_mul) * self.t_initial
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else:
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i = t // self.t_initial
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t_i = self.t_initial
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t_curr = t - (self.t_initial * i)
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gamma = self.decay_rate ** i
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lr_min = self.lr_min * gamma
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lr_max_values = [v * gamma for v in self.base_values]
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if self.cycle_limit == 0 or (self.cycle_limit > 0 and i < self.cycle_limit):
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lrs = [
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lr_min + 0.5 * (lr_max - lr_min) * (1 + math.cos(math.pi * t_curr / t_i)) for lr_max in lr_max_values
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]
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else:
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lrs = [self.lr_min for _ in self.base_values]
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return lrs
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def get_epoch_values(self, epoch: int):
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if self.t_in_epochs:
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return self._get_lr(epoch)
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else:
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return None
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def get_update_values(self, num_updates: int):
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if not self.t_in_epochs:
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return self._get_lr(num_updates)
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else:
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return None
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def get_cycle_length(self, cycles=0):
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if not cycles:
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cycles = self.cycle_limit
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assert cycles > 0
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if self.t_mul == 1.0:
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return self.t_initial * cycles
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else:
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return int(math.floor(-self.t_initial * (self.t_mul ** cycles - 1) / (1 - self.t_mul)))
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