ColossalAI/colossalai/nn/optimizer/lamb.py

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"""
Adapted from the pytorch-lamb library at https://github.com/cybertronai/pytorch-lamb
"""
import torch
from torch.optim import Optimizer
class Lamb(Optimizer):
r"""Implements Lamb algorithm.
It has been proposed in `Large Batch Optimization for Deep Learning: Training BERT in 76 minutes`_.
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Arguments:
params (iterable): iterable of parameters to optimize or dicts defining
parameter groups
lr (float, optional): learning rate (default: 1e-3)
betas (Tuple[float, float], optional): coefficients used for computing
running averages of gradient and its square (default: (0.9, 0.999))
eps (float, optional): term added to the denominator to improve
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numerical stability (default: 1e-6)
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weight_decay (float, optional): weight decay (L2 penalty) (default: 0)
adam (bool, optional): always use trust ratio = 1, which turns this into
Adam. Useful for comparison purposes.
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.. _Large Batch Optimization for Deep Learning\: Training BERT in 76 minutes:
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https://arxiv.org/abs/1904.00962
"""
def __init__(self, params, lr=1e-3, betas=(0.9, 0.999), eps=1e-6, weight_decay=0, adam=False):
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if not 0.0 <= lr:
raise ValueError("Invalid learning rate: {}".format(lr))
if not 0.0 <= eps:
raise ValueError("Invalid epsilon value: {}".format(eps))
if not 0.0 <= betas[0] < 1.0:
raise ValueError("Invalid beta parameter at index 0: {}".format(betas[0]))
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if not 0.0 <= betas[1] < 1.0:
raise ValueError("Invalid beta parameter at index 1: {}".format(betas[1]))
defaults = dict(lr=lr, betas=betas, eps=eps, weight_decay=weight_decay)
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self.adam = adam
super(Lamb, self).__init__(params, defaults)
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:
for p in group['params']:
if p.grad is None:
continue
grad = p.grad.data
if grad.is_sparse:
raise RuntimeError('Lamb does not support sparse gradients, consider SparseAdam instead.')
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state = self.state[p]
# State initialization
if len(state) == 0:
state['step'] = 0
# Exponential moving average of gradient values
state['exp_avg'] = torch.zeros_like(p)
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# Exponential moving average of squared gradient values
state['exp_avg_sq'] = torch.zeros_like(p)
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exp_avg, exp_avg_sq = state['exp_avg'], state['exp_avg_sq']
beta1, beta2 = group['betas']
state['step'] += 1
# Decay the first and second moment running average coefficient
# m_t
exp_avg.mul_(beta1).add_(grad, alpha=1 - beta1)
# v_t
exp_avg_sq.mul_(beta2).addcmul_(grad, grad, value=1 - beta2)
# Paper v3 does not use debiasing.
# bias_correction1 = 1 - beta1 ** state['step']
# bias_correction2 = 1 - beta2 ** state['step']
# Apply bias to lr to avoid broadcast.
# * math.sqrt(bias_correction2) / bias_correction1
step_size = group['lr']
weight_norm = p.data.pow(2).sum().sqrt()
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adam_step = exp_avg / exp_avg_sq.sqrt().add(group['eps'])
if group['weight_decay'] != 0:
adam_step.add_(p.data, alpha=group['weight_decay'])
adam_norm = adam_step.pow(2).sum().sqrt()
if weight_norm == 0 or adam_norm == 0:
trust_ratio = 1
else:
trust_ratio = weight_norm / adam_norm
state['weight_norm'] = weight_norm
state['adam_norm'] = adam_norm
state['trust_ratio'] = trust_ratio
if self.adam:
trust_ratio = 1
p.data.add_(adam_step, alpha=-step_size * trust_ratio)
return loss