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# Copyright (c) Meta Platforms, Inc. and affiliates. | ||
# All rights reserved. | ||
# | ||
# This source code is licensed under the license found in the | ||
# LICENSE file in the root directory of this source tree. | ||
import torch | ||
import torch.optim | ||
import math | ||
|
||
class AdamWScheduleFree(torch.optim.Optimizer): | ||
r""" | ||
Schedule-Free AdamW | ||
As the name suggests, no scheduler is needed with this optimizer. | ||
To add warmup, rather than using a learning rate schedule you can just | ||
set the warmup_steps parameter. | ||
This optimizer requires that .train() and .val() be called before the | ||
beginning of training and evaluation respectively. | ||
Arguments: | ||
params (iterable): | ||
Iterable of parameters to optimize or dicts defining | ||
parameter groups. | ||
lr (float): | ||
Learning rate parameter (default 0.0025) | ||
betas (Tuple[float, float], optional): coefficients used for computing | ||
running averages of gradient and its square (default: (0.9, 0.999)). | ||
eps (float): | ||
Term added to the denominator outside of the root operation to | ||
improve numerical stability. (default: 1e-8). | ||
weight_decay (float): | ||
Weight decay, i.e. a L2 penalty (default: 0). | ||
warmup_steps (int): Enables a linear learning rate warmup (default 0). | ||
r (float): Use polynomial weighting in the average | ||
with power r (default 0). | ||
weight_lr_power (float): During warmup, the weights in the average will | ||
be equal to lr raised to this power. Set to 0 for no weighting | ||
(default 2.0). | ||
""" | ||
def __init__(self, | ||
params, | ||
lr=0.0025, | ||
betas=(0.9, 0.999), | ||
eps=1e-8, | ||
weight_decay=0, | ||
warmup_steps=0, | ||
r=0.0, | ||
weight_lr_power=2.0, | ||
): | ||
|
||
defaults = dict(lr=lr, | ||
betas=betas, | ||
eps=eps, | ||
r=r, | ||
k=0, | ||
warmup_steps=warmup_steps, | ||
train_mode = True, | ||
weight_sum=0.0, | ||
lr_max=-1.0, | ||
weight_lr_power=weight_lr_power, | ||
weight_decay=weight_decay) | ||
super().__init__(params, defaults) | ||
|
||
def eval(self): | ||
for group in self.param_groups: | ||
train_mode = group['train_mode'] | ||
beta1, _ = group['betas'] | ||
if train_mode: | ||
for p in group['params']: | ||
state = self.state[p] | ||
if 'z' in state: | ||
# Set p.data to x | ||
p.data.lerp_(end=state['z'], weight=1-1/beta1) | ||
group['train_mode'] = False | ||
|
||
def train(self): | ||
for group in self.param_groups: | ||
train_mode = group['train_mode'] | ||
beta1, _ = group['betas'] | ||
if not train_mode: | ||
for p in group['params']: | ||
state = self.state[p] | ||
if 'z' in state: | ||
# Set p.data to y | ||
p.data.lerp_(end=state['z'], weight=1-beta1) | ||
group['train_mode'] = True | ||
|
||
def step(self, closure=None): | ||
"""Performs a single optimization step. | ||
Arguments: | ||
closure (callable, optional): A closure that reevaluates the model | ||
and returns the loss. | ||
""" | ||
|
||
loss = None | ||
if closure is not None: | ||
loss = closure() | ||
|
||
for group in self.param_groups: | ||
eps = group['eps'] | ||
beta1, beta2 = group['betas'] | ||
decay = group['weight_decay'] | ||
k = group['k'] | ||
r = group['r'] | ||
warmup_steps = group['warmup_steps'] | ||
weight_lr_power = group['weight_lr_power'] | ||
|
||
if k < warmup_steps: | ||
sched = (k+1) / warmup_steps | ||
else: | ||
sched = 1.0 | ||
|
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bias_correction2 = 1 - beta2 ** (k+1) | ||
lr = group['lr']*sched*math.sqrt(bias_correction2) | ||
|
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lr_max = group['lr_max'] = max(lr, group['lr_max']) | ||
|
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weight = ((k+1)**r) * (lr_max**weight_lr_power) | ||
weight_sum = group['weight_sum'] = group['weight_sum'] + weight | ||
|
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ckp1 = weight/weight_sum | ||
|
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if not group['train_mode']: | ||
raise Exception("Not in train mode!") | ||
|
||
for p in group['params']: | ||
if p.grad is None: | ||
continue | ||
|
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y = p.data # Notation to match theory | ||
grad = p.grad.data | ||
|
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state = self.state[p] | ||
|
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if 'z' not in state: | ||
state['z'] = torch.clone(y) | ||
state['exp_avg_sq'] = torch.zeros_like(p.data) | ||
|
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z = state['z'] | ||
exp_avg_sq = state['exp_avg_sq'] | ||
|
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exp_avg_sq.mul_(beta2).addcmul_(grad, grad, value=1-beta2) | ||
denom = exp_avg_sq.sqrt().add_(eps) | ||
|
||
# Reuse grad buffer for memory efficiency | ||
grad_normalized = grad.div_(denom) | ||
|
||
# Weight decay calculated at y | ||
if decay != 0: | ||
grad_normalized.add_(y, alpha=decay) | ||
|
||
# These operations update y in-place, | ||
# without computing x explicitly. | ||
y.lerp_(end=z, weight=ckp1) | ||
y.add_(grad_normalized, alpha=lr*(beta1*(1-ckp1)-1)) | ||
|
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# z step | ||
z.sub_(grad_normalized, alpha=lr) | ||
|
||
group['k'] = k+1 | ||
return loss |
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class NoSchedule(): | ||
"""No Schedule | ||
""" | ||
def __init__(self, | ||
optimizer, | ||
last_epoch=-1): | ||
self.last_epoch=0 if last_epoch<0 else last_epoch | ||
|
||
def step(self): | ||
self.last_epoch+=1 | ||
|
||
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