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import math
import torch
from torch.optim.lr_scheduler import _LRScheduler
class CosineAnnealingWarmupRestarts(_LRScheduler):
"""
optimizer (Optimizer): Wrapped optimizer.
first_cycle_steps (int): First cycle step size.
cycle_mult(float): Cycle steps magnification. Default: -1.
max_lr(float): First cycle's max learning rate. Default: 0.1.
min_lr(float): Min learning rate. Default: 0.001.
warmup_steps(int): Linear warmup step size. Default: 0.
gamma(float): Decrease rate of max learning rate by cycle. Default: 1.
last_epoch (int): The index of last epoch. Default: -1.
"""
def __init__(self,
optimizer : torch.optim.Optimizer,
first_cycle_steps : int,
cycle_mult : float = 1.,
max_lr : float = 0.1,
min_lr : float = 0.001,
warmup_steps : int = 0,
gamma : float = 1.,
last_epoch : int = -1
):
assert warmup_steps < first_cycle_steps
self.first_cycle_steps = first_cycle_steps # first cycle step size
self.cycle_mult = cycle_mult # cycle steps magnification
self.base_max_lr = max_lr # first max learning rate
self.max_lr = max_lr # max learning rate in the current cycle
self.min_lr = min_lr # min learning rate
self.warmup_steps = warmup_steps # warmup step size
self.gamma = gamma # decrease rate of max learning rate by cycle
self.cur_cycle_steps = first_cycle_steps # first cycle step size
self.cycle = 0 # cycle count
self.step_in_cycle = last_epoch # step size of the current cycle
super(CosineAnnealingWarmupRestarts, self).__init__(optimizer, last_epoch)
# set learning rate min_lr
self.init_lr()
def init_lr(self):
self.base_lrs = []
for param_group in self.optimizer.param_groups:
param_group['lr'] = self.min_lr
self.base_lrs.append(self.min_lr)
def get_lr(self):
if self.step_in_cycle == -1:
return self.base_lrs
elif self.step_in_cycle < self.warmup_steps:
return [(self.max_lr - base_lr)*self.step_in_cycle / self.warmup_steps + base_lr for base_lr in self.base_lrs]
else:
# return [self.max_lr] * len(self.base_lrs)
return [base_lr + (self.max_lr - base_lr) \
* (1 + math.cos(math.pi * (self.step_in_cycle-self.warmup_steps) \
/ (self.cur_cycle_steps - self.warmup_steps))) / 2
for base_lr in self.base_lrs]
def step(self, epoch=None):
if epoch is None:
epoch = self.last_epoch + 1
self.step_in_cycle = self.step_in_cycle + 1
if self.step_in_cycle >= self.cur_cycle_steps:
self.cycle += 1
self.step_in_cycle = self.step_in_cycle - self.cur_cycle_steps
self.cur_cycle_steps = int((self.cur_cycle_steps - self.warmup_steps) * self.cycle_mult) + self.warmup_steps
else:
if epoch >= self.first_cycle_steps:
if self.cycle_mult == 1.:
self.step_in_cycle = epoch % self.first_cycle_steps
self.cycle = epoch // self.first_cycle_steps
else:
n = int(math.log((epoch / self.first_cycle_steps * (self.cycle_mult - 1) + 1), self.cycle_mult))
self.cycle = n
self.step_in_cycle = epoch - int(self.first_cycle_steps * (self.cycle_mult ** n - 1) / (self.cycle_mult - 1))
self.cur_cycle_steps = self.first_cycle_steps * self.cycle_mult ** (n)
else:
self.cur_cycle_steps = self.first_cycle_steps
self.step_in_cycle = epoch
self.max_lr = self.base_max_lr * (self.gamma**self.cycle)
self.last_epoch = math.floor(epoch)
for param_group, lr in zip(self.optimizer.param_groups, self.get_lr()):
param_group['lr'] = lr
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