/
clr.py
executable file
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/
clr.py
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import numpy as np
class CyclicLR(object):
def __init__(self, optimizer, base_lr=1e-3, max_lr=6e-3,
step_size=2000, mode='triangular', gamma=1.,
scale_fn=None, scale_mode='cycle', last_batch_iteration=-1):
self.optimizer = optimizer
if isinstance(base_lr, list) or isinstance(base_lr, tuple):
if len(base_lr) != len(optimizer.param_groups):
raise ValueError("expected {} base_lr, got {}".format(
len(optimizer.param_groups), len(base_lr)))
self.base_lrs = list(base_lr)
else:
self.base_lrs = [base_lr] * len(optimizer.param_groups)
if isinstance(max_lr, list) or isinstance(max_lr, tuple):
if len(max_lr) != len(optimizer.param_groups):
raise ValueError("expected {} max_lr, got {}".format(
len(optimizer.param_groups), len(max_lr)))
self.max_lrs = list(max_lr)
else:
self.max_lrs = [max_lr] * len(optimizer.param_groups)
self.step_size = step_size
if mode not in ['triangular', 'triangular2', 'exp_range'] \
and scale_fn is None:
raise ValueError('mode is invalid and scale_fn is None')
self.mode = mode
self.gamma = gamma
if scale_fn is None:
if self.mode == 'triangular':
self.scale_fn = self._triangular_scale_fn
self.scale_mode = 'cycle'
elif self.mode == 'triangular2':
self.scale_fn = self._triangular2_scale_fn
self.scale_mode = 'cycle'
elif self.mode == 'exp_range':
self.scale_fn = self._exp_range_scale_fn
self.scale_mode = 'iterations'
else:
self.scale_fn = scale_fn
self.scale_mode = scale_mode
self.batch_step(last_batch_iteration + 1)
self.last_batch_iteration = last_batch_iteration
def batch_step(self, batch_iteration=None):
if batch_iteration is None:
batch_iteration = self.last_batch_iteration + 1
self.last_batch_iteration = batch_iteration
for param_group, lr in zip(self.optimizer.param_groups, self.get_lr()):
param_group['lr'] = lr
def _triangular_scale_fn(self, x):
return 1.
def _triangular2_scale_fn(self, x):
return 1 / (2. ** (x - 1))
def _exp_range_scale_fn(self, x):
return self.gamma**(x)
def get_lr(self):
step_size = float(self.step_size)
cycle = np.floor(1 + self.last_batch_iteration / (2 * step_size))
x = np.abs(self.last_batch_iteration / step_size - 2 * cycle + 1)
lrs = []
param_lrs = zip(self.optimizer.param_groups, self.base_lrs, self.max_lrs)
for param_group, base_lr, max_lr in param_lrs:
base_height = (max_lr - base_lr) * np.maximum(0, (1 - x))
if self.scale_mode == 'cycle':
lr = base_lr + base_height * self.scale_fn(cycle)
else:
lr = base_lr + base_height * self.scale_fn(self.last_batch_iteration)
lrs.append(lr)
return lrs