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# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
from dataclasses import dataclass, field
from typing import Optional, List
from omegaconf import II
from fairseq.dataclass import FairseqDataclass
from fairseq.optim.lr_scheduler import FairseqLRScheduler, register_lr_scheduler
@dataclass
class FixedLRScheduleConfig(FairseqDataclass):
force_anneal: Optional[int] = field(
default=None,
metadata={"help": "force annealing at specified epoch"},
)
lr_shrink: float = field(
default=0.1,
metadata={"help": "shrink factor for annealing, lr_new = (lr * lr_shrink)"},
)
warmup_updates: int = field(
default=0,
metadata={"help": "warmup the learning rate linearly for the first N updates"},
)
lr: List[float] = II("optimization.lr")
@register_lr_scheduler("fixed", dataclass=FixedLRScheduleConfig)
class FixedLRSchedule(FairseqLRScheduler):
"""Decay the LR on a fixed schedule."""
def __init__(self, cfg: FixedLRScheduleConfig, optimizer):
super().__init__(cfg, optimizer)
self.lr = cfg.lr[0]
if cfg.warmup_updates > 0:
self.warmup_factor = 1.0 / cfg.warmup_updates
else:
self.warmup_factor = 1
def state_dict(self):
return {"lr": self.lr}
def load_state_dict(self, state_dict):
if "lr" in state_dict:
self.lr = state_dict["lr"]
def get_next_lr(self, epoch):
lrs = self.cfg.lr
if self.cfg.force_anneal is None or epoch < self.cfg.force_anneal:
# use fixed LR schedule
next_lr = lrs[min(epoch - 1, len(lrs) - 1)]
else:
# annneal based on lr_shrink
next_lr = lrs[-1] * self.cfg.lr_shrink ** (
epoch + 1 - self.cfg.force_anneal
)
return next_lr
def step_begin_epoch(self, epoch):
"""Update the learning rate at the beginning of the given epoch."""
self.lr = self.get_next_lr(epoch)
self.optimizer.set_lr(self.warmup_factor * self.lr)
return self.optimizer.get_lr()
def step_update(self, num_updates):
"""Update the learning rate after each update."""
if self.cfg.warmup_updates > 0 and num_updates < self.cfg.warmup_updates:
self.warmup_factor = (num_updates + 1) / float(self.cfg.warmup_updates)
self.optimizer.set_lr(self.warmup_factor * self.lr)
else:
self.optimizer.set_lr(self.lr)
return self.optimizer.get_lr()
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