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""" Plateau Scheduler
Adapts PyTorch plateau scheduler and allows application of noise, warmup.
Hacked together by / Copyright 2020 Ross Wightman
"""
import torch
from .scheduler import Scheduler
class PlateauLRScheduler(Scheduler):
"""Decay the LR by a factor every time the validation loss plateaus."""
def __init__(self,
optimizer,
decay_rate=0.1,
patience_t=10,
verbose=True,
threshold=1e-4,
cooldown_t=0,
warmup_t=0,
warmup_lr_init=0,
lr_min=0,
mode='max',
noise_range_t=None,
noise_type='normal',
noise_pct=0.67,
noise_std=1.0,
noise_seed=None,
initialize=True,
):
super().__init__(optimizer, 'lr', initialize=initialize)
self.lr_scheduler = torch.optim.lr_scheduler.ReduceLROnPlateau(
self.optimizer,
patience=patience_t,
factor=decay_rate,
verbose=verbose,
threshold=threshold,
cooldown=cooldown_t,
mode=mode,
min_lr=lr_min
)
self.noise_range = noise_range_t
self.noise_pct = noise_pct
self.noise_type = noise_type
self.noise_std = noise_std
self.noise_seed = noise_seed if noise_seed is not None else 42
self.warmup_t = warmup_t
self.warmup_lr_init = warmup_lr_init
if self.warmup_t:
self.warmup_steps = [(v - warmup_lr_init) / self.warmup_t for v in self.base_values]
super().update_groups(self.warmup_lr_init)
else:
self.warmup_steps = [1 for _ in self.base_values]
self.restore_lr = None
def state_dict(self):
return {
'best': self.lr_scheduler.best,
'last_epoch': self.lr_scheduler.last_epoch,
}
def load_state_dict(self, state_dict):
self.lr_scheduler.best = state_dict['best']
if 'last_epoch' in state_dict:
self.lr_scheduler.last_epoch = state_dict['last_epoch']
# override the base class step fn completely
def step(self, epoch, metric=None):
if epoch <= self.warmup_t:
lrs = [self.warmup_lr_init + epoch * s for s in self.warmup_steps]
super().update_groups(lrs)
else:
if self.restore_lr is not None:
# restore actual LR from before our last noise perturbation before stepping base
for i, param_group in enumerate(self.optimizer.param_groups):
param_group['lr'] = self.restore_lr[i]
self.restore_lr = None
self.lr_scheduler.step(metric, epoch) # step the base scheduler
if self.noise_range is not None:
if isinstance(self.noise_range, (list, tuple)):
apply_noise = self.noise_range[0] <= epoch < self.noise_range[1]
else:
apply_noise = epoch >= self.noise_range
if apply_noise:
self._apply_noise(epoch)
def _apply_noise(self, epoch):
g = torch.Generator()
g.manual_seed(self.noise_seed + epoch)
if self.noise_type == 'normal':
while True:
# resample if noise out of percent limit, brute force but shouldn't spin much
noise = torch.randn(1, generator=g).item()
if abs(noise) < self.noise_pct:
break
else:
noise = 2 * (torch.rand(1, generator=g).item() - 0.5) * self.noise_pct
# apply the noise on top of previous LR, cache the old value so we can restore for normal
# stepping of base scheduler
restore_lr = []
for i, param_group in enumerate(self.optimizer.param_groups):
old_lr = float(param_group['lr'])
restore_lr.append(old_lr)
new_lr = old_lr + old_lr * noise
param_group['lr'] = new_lr
self.restore_lr = restore_lr
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