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# Copyright 2020 - 2021 MONAI Consortium
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import math
import warnings
from typing import List
from torch.optim import Adam, Optimizer
from torch.optim.lr_scheduler import _LRScheduler
class LinearWarmupCosineAnnealingLR(_LRScheduler):
def __init__(
self,
optimizer: Optimizer,
warmup_epochs: int,
max_epochs: int,
warmup_start_lr: float = 0.0,
eta_min: float = 0.0,
last_epoch: int = -1,
) -> None:
"""
Args:
optimizer (Optimizer): Wrapped optimizer.
warmup_epochs (int): Maximum number of iterations for linear warmup
max_epochs (int): Maximum number of iterations
warmup_start_lr (float): Learning rate to start the linear warmup. Default: 0.
eta_min (float): Minimum learning rate. Default: 0.
last_epoch (int): The index of last epoch. Default: -1.
"""
self.warmup_epochs = warmup_epochs
self.max_epochs = max_epochs
self.warmup_start_lr = warmup_start_lr
self.eta_min = eta_min
super(LinearWarmupCosineAnnealingLR, self).__init__(optimizer, last_epoch)
def get_lr(self) -> List[float]:
"""
Compute learning rate using chainable form of the scheduler
"""
if not self._get_lr_called_within_step:
warnings.warn(
"To get the last learning rate computed by the scheduler, " "please use `get_last_lr()`.", UserWarning
)
if self.last_epoch == 0:
return [self.warmup_start_lr] * len(self.base_lrs)
elif self.last_epoch < self.warmup_epochs:
return [
group["lr"] + (base_lr - self.warmup_start_lr) / (self.warmup_epochs - 1)
for base_lr, group in zip(self.base_lrs, self.optimizer.param_groups)
]
elif self.last_epoch == self.warmup_epochs:
return self.base_lrs
elif (self.last_epoch - 1 - self.max_epochs) % (2 * (self.max_epochs - self.warmup_epochs)) == 0:
return [
group["lr"]
+ (base_lr - self.eta_min) * (1 - math.cos(math.pi / (self.max_epochs - self.warmup_epochs))) / 2
for base_lr, group in zip(self.base_lrs, self.optimizer.param_groups)
]
return [
(1 + math.cos(math.pi * (self.last_epoch - self.warmup_epochs) / (self.max_epochs - self.warmup_epochs)))
/ (
1
+ math.cos(
math.pi * (self.last_epoch - self.warmup_epochs - 1) / (self.max_epochs - self.warmup_epochs)
)
)
* (group["lr"] - self.eta_min)
+ self.eta_min
for group in self.optimizer.param_groups
]
def _get_closed_form_lr(self) -> List[float]:
"""
Called when epoch is passed as a param to the `step` function of the scheduler.
"""
if self.last_epoch < self.warmup_epochs:
return [
self.warmup_start_lr + self.last_epoch * (base_lr - self.warmup_start_lr) / (self.warmup_epochs - 1)
for base_lr in self.base_lrs
]
return [
self.eta_min
+ 0.5
* (base_lr - self.eta_min)
* (1 + math.cos(math.pi * (self.last_epoch - self.warmup_epochs) / (self.max_epochs - self.warmup_epochs)))
for base_lr in self.base_lrs
]
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