from bisect import bisect_right
from .optimizer import Optimizer
class _LRScheduler(object):
def __init__(self, optimizer, last_epoch=-1):
if not isinstance(optimizer, Optimizer):
raise TypeError('{} is not an Optimizer'.format(
type(optimizer).__name__))
self.optimizer = optimizer
if last_epoch == -1:
for group in optimizer.param_groups:
group.setdefault('initial_lr', group['lr'])
else:
for i, group in enumerate(optimizer.param_groups):
if 'initial_lr' not in group:
raise KeyError("param 'initial_lr' is not specified "
"in param_groups[{}] when resuming an optimizer".format(i))
self.base_lrs = list(map(lambda group: group['initial_lr'], optimizer.param_groups))
self.step(last_epoch + 1)
self.last_epoch = last_epoch
def get_lr(self):
raise NotImplementedError
def step(self, epoch=None):
if epoch is None:
epoch = self.last_epoch + 1
self.last_epoch = epoch
for param_group, lr in zip(self.optimizer.param_groups, self.get_lr()):
param_group['lr'] = lr
[docs]class LambdaLR(_LRScheduler):
"""Sets the learning rate of each parameter group to the initial lr
times a given function. When last_epoch=-1, sets initial lr as lr.
Args:
optimizer (Optimizer): Wrapped optimizer.
lr_lambda (function or list): A function which computes a multiplicative
factor given an integer parameter epoch, or a list of such
functions, one for each group in optimizer.param_groups.
last_epoch (int): The index of last epoch. Default: -1.
Example:
>>> # Assuming optimizer has two groups.
>>> lambda1 = lambda epoch: epoch // 30
>>> lambda2 = lambda epoch: 0.95 ** epoch
>>> scheduler = LambdaLR(optimizer, lr_lambda=[lambda1, lambda2])
>>> for epoch in range(100):
>>> scheduler.step()
>>> train(...)
>>> validate(...)
"""
def __init__(self, optimizer, lr_lambda, last_epoch=-1):
self.optimizer = optimizer
if not isinstance(lr_lambda, list) and not isinstance(lr_lambda, tuple):
self.lr_lambdas = [lr_lambda] * len(optimizer.param_groups)
else:
if len(lr_lambda) != len(optimizer.param_groups):
raise ValueError("Expected {} lr_lambdas, but got {}".format(
len(optimizer.param_groups), len(lr_lambda)))
self.lr_lambdas = list(lr_lambda)
self.last_epoch = last_epoch
super(LambdaLR, self).__init__(optimizer, last_epoch)
def get_lr(self):
return [base_lr * lmbda(self.last_epoch)
for lmbda, base_lr in zip(self.lr_lambdas, self.base_lrs)]
[docs]class StepLR(_LRScheduler):
"""Sets the learning rate of each parameter group to the initial lr
decayed by gamma every step_size epochs. When last_epoch=-1, sets
initial lr as lr.
Args:
optimizer (Optimizer): Wrapped optimizer.
step_size (int): Period of learning rate decay.
gamma (float): Multiplicative factor of learning rate decay.
Default: 0.1.
last_epoch (int): The index of last epoch. Default: -1.
Example:
>>> # Assuming optimizer uses lr = 0.5 for all groups
>>> # lr = 0.05 if epoch < 30
>>> # lr = 0.005 if 30 <= epoch < 60
>>> # lr = 0.0005 if 60 <= epoch < 90
>>> # ...
>>> scheduler = StepLR(optimizer, step_size=30, gamma=0.1)
>>> for epoch in range(100):
>>> scheduler.step()
>>> train(...)
>>> validate(...)
"""
def __init__(self, optimizer, step_size, gamma=0.1, last_epoch=-1):
self.step_size = step_size
self.gamma = gamma
super(StepLR, self).__init__(optimizer, last_epoch)
def get_lr(self):
return [base_lr * self.gamma ** (self.last_epoch // self.step_size)
for base_lr in self.base_lrs]
[docs]class MultiStepLR(_LRScheduler):
"""Set the learning rate of each parameter group to the initial lr decayed
by gamma once the number of epoch reaches one of the milestones. When
last_epoch=-1, sets initial lr as lr.
Args:
optimizer (Optimizer): Wrapped optimizer.
milestones (list): List of epoch indices. Must be increasing.
gamma (float): Multiplicative factor of learning rate decay.
Default: 0.1.
last_epoch (int): The index of last epoch. Default: -1.
Example:
>>> # Assuming optimizer uses lr = 0.5 for all groups
>>> # lr = 0.05 if epoch < 30
>>> # lr = 0.005 if 30 <= epoch < 80
>>> # lr = 0.0005 if epoch >= 80
>>> scheduler = MultiStepLR(optimizer, milestones=[30,80], gamma=0.1)
>>> for epoch in range(100):
>>> scheduler.step()
>>> train(...)
>>> validate(...)
"""
def __init__(self, optimizer, milestones, gamma=0.1, last_epoch=-1):
if not list(milestones) == sorted(milestones):
raise ValueError('Milestones should be a list of'
' increasing integers. Got {}', milestones)
self.milestones = milestones
self.gamma = gamma
super(MultiStepLR, self).__init__(optimizer, last_epoch)
def get_lr(self):
return [base_lr * self.gamma ** bisect_right(self.milestones, self.last_epoch)
for base_lr in self.base_lrs]
[docs]class ExponentialLR(_LRScheduler):
"""Set the learning rate of each parameter group to the initial lr decayed
by gamma every epoch. When last_epoch=-1, sets initial lr as lr.
Args:
optimizer (Optimizer): Wrapped optimizer.
gamma (float): Multiplicative factor of learning rate decay.
last_epoch (int): The index of last epoch. Default: -1.
"""
def __init__(self, optimizer, gamma, last_epoch=-1):
self.gamma = gamma
super(ExponentialLR, self).__init__(optimizer, last_epoch)
def get_lr(self):
return [base_lr * self.gamma ** self.last_epoch
for base_lr in self.base_lrs]
[docs]class ReduceLROnPlateau(object):
"""Reduce learning rate when a metric has stopped improving.
Models often benefit from reducing the learning rate by a factor
of 2-10 once learning stagnates. This scheduler reads a metrics
quantity and if no improvement is seen for a 'patience' number
of epochs, the learning rate is reduced.
Args:
optimizer (Optimizer): Wrapped optimizer.
mode (str): One of `min`, `max`. In `min` mode, lr will
be reduced when the quantity monitored has stopped
decreasing; in `max` mode it will be reduced when the
quantity monitored has stopped increasing. Default: 'min'.
factor (float): Factor by which the learning rate will be
reduced. new_lr = lr * factor. Default: 0.1.
patience (int): Number of epochs with no improvement after
which learning rate will be reduced. Default: 10.
verbose (bool): If ``True``, prints a message to stdout for
each update. Default: ``False``.
threshold (float): Threshold for measuring the new optimum,
to only focus on significant changes. Default: 1e-4.
threshold_mode (str): One of `rel`, `abs`. In `rel` mode,
dynamic_threshold = best * ( 1 + threshold ) in 'max'
mode or best * ( 1 - threshold ) in `min` mode.
In `abs` mode, dynamic_threshold = best + threshold in
`max` mode or best - threshold in `min` mode. Default: 'rel'.
cooldown (int): Number of epochs to wait before resuming
normal operation after lr has been reduced. Default: 0.
min_lr (float or list): A scalar or a list of scalars. A
lower bound on the learning rate of all param groups
or each group respectively. Default: 0.
eps (float): Minimal decay applied to lr. If the difference
between new and old lr is smaller than eps, the update is
ignored. Default: 1e-8.
Example:
>>> optimizer = torch.optim.SGD(model.parameters(), lr=0.1, momentum=0.9)
>>> scheduler = ReduceLROnPlateau(optimizer, 'min')
>>> for epoch in range(10):
>>> train(...)
>>> val_loss = validate(...)
>>> # Note that step should be called after validate()
>>> scheduler.step(val_loss)
"""
def __init__(self, optimizer, mode='min', factor=0.1, patience=10,
verbose=False, threshold=1e-4, threshold_mode='rel',
cooldown=0, min_lr=0, eps=1e-8):
if factor >= 1.0:
raise ValueError('Factor should be < 1.0.')
self.factor = factor
if not isinstance(optimizer, Optimizer):
raise TypeError('{} is not an Optimizer'.format(
type(optimizer).__name__))
self.optimizer = optimizer
if isinstance(min_lr, list) or isinstance(min_lr, tuple):
if len(min_lr) != len(optimizer.param_groups):
raise ValueError("expected {} min_lrs, got {}".format(
len(optimizer.param_groups), len(min_lr)))
self.min_lrs = list(min_lr)
else:
self.min_lrs = [min_lr] * len(optimizer.param_groups)
self.patience = patience
self.verbose = verbose
self.cooldown = cooldown
self.cooldown_counter = 0
self.mode = mode
self.threshold = threshold
self.threshold_mode = threshold_mode
self.best = None
self.num_bad_epochs = None
self.mode_worse = None # the worse value for the chosen mode
self.is_better = None
self.eps = eps
self.last_epoch = -1
self._init_is_better(mode=mode, threshold=threshold,
threshold_mode=threshold_mode)
self._reset()
def _reset(self):
"""Resets num_bad_epochs counter and cooldown counter."""
self.best = self.mode_worse
self.cooldown_counter = 0
self.num_bad_epochs = 0
def step(self, metrics, epoch=None):
current = metrics
if epoch is None:
epoch = self.last_epoch = self.last_epoch + 1
self.last_epoch = epoch
if self.is_better(current, self.best):
self.best = current
self.num_bad_epochs = 0
else:
self.num_bad_epochs += 1
if self.in_cooldown:
self.cooldown_counter -= 1
self.num_bad_epochs = 0 # ignore any bad epochs in cooldown
if self.num_bad_epochs > self.patience:
self._reduce_lr(epoch)
self.cooldown_counter = self.cooldown
self.num_bad_epochs = 0
def _reduce_lr(self, epoch):
for i, param_group in enumerate(self.optimizer.param_groups):
old_lr = float(param_group['lr'])
new_lr = max(old_lr * self.factor, self.min_lrs[i])
if old_lr - new_lr > self.eps:
param_group['lr'] = new_lr
if self.verbose:
print('Epoch {:5d}: reducing learning rate'
' of group {} to {:.4e}.'.format(epoch, i, new_lr))
@property
def in_cooldown(self):
return self.cooldown_counter > 0
def _init_is_better(self, mode, threshold, threshold_mode):
if mode not in {'min', 'max'}:
raise ValueError('mode ' + mode + ' is unknown!')
if threshold_mode not in {'rel', 'abs'}:
raise ValueError('threshold mode ' + mode + ' is unknown!')
if mode == 'min' and threshold_mode == 'rel':
rel_epsilon = 1. - threshold
self.is_better = lambda a, best: a < best * rel_epsilon
self.mode_worse = float('Inf')
elif mode == 'min' and threshold_mode == 'abs':
self.is_better = lambda a, best: a < best - threshold
self.mode_worse = float('Inf')
elif mode == 'max' and threshold_mode == 'rel':
rel_epsilon = threshold + 1.
self.is_better = lambda a, best: a > best * rel_epsilon
self.mode_worse = -float('Inf')
else: # mode == 'max' and epsilon_mode == 'abs':
self.is_better = lambda a, best: a > best + threshold
self.mode_worse = -float('Inf')