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"""RAdam Optimizer.
Implementation lifted from: https://github.com/LiyuanLucasLiu/RAdam
Paper: `On the Variance of the Adaptive Learning Rate and Beyond` - https://arxiv.org/abs/1908.03265
"""
import math
import torch
from torch.optim.optimizer import Optimizer
class RAdam(Optimizer):
def __init__(self, params, lr=1e-3, betas=(0.9, 0.999), eps=1e-8, weight_decay=0):
defaults = dict(
lr=lr, betas=betas, eps=eps, weight_decay=weight_decay,
buffer=[[None, None, None] for _ in range(10)])
super(RAdam, self).__init__(params, defaults)
def __setstate__(self, state):
super(RAdam, self).__setstate__(state)
@torch.no_grad()
def step(self, closure=None):
loss = None
if closure is not None:
with torch.enable_grad():
loss = closure()
for group in self.param_groups:
for p in group['params']:
if p.grad is None:
continue
grad = p.grad.float()
if grad.is_sparse:
raise RuntimeError('RAdam does not support sparse gradients')
p_fp32 = p.float()
state = self.state[p]
if len(state) == 0:
state['step'] = 0
state['exp_avg'] = torch.zeros_like(p_fp32)
state['exp_avg_sq'] = torch.zeros_like(p_fp32)
else:
state['exp_avg'] = state['exp_avg'].type_as(p_fp32)
state['exp_avg_sq'] = state['exp_avg_sq'].type_as(p_fp32)
exp_avg, exp_avg_sq = state['exp_avg'], state['exp_avg_sq']
beta1, beta2 = group['betas']
exp_avg_sq.mul_(beta2).addcmul_(grad, grad, value=1 - beta2)
exp_avg.mul_(beta1).add_(grad, alpha=1 - beta1)
state['step'] += 1
buffered = group['buffer'][int(state['step'] % 10)]
if state['step'] == buffered[0]:
num_sma, step_size = buffered[1], buffered[2]
else:
buffered[0] = state['step']
beta2_t = beta2 ** state['step']
num_sma_max = 2 / (1 - beta2) - 1
num_sma = num_sma_max - 2 * state['step'] * beta2_t / (1 - beta2_t)
buffered[1] = num_sma
# more conservative since it's an approximated value
if num_sma >= 5:
step_size = group['lr'] * math.sqrt(
(1 - beta2_t) *
(num_sma - 4) / (num_sma_max - 4) *
(num_sma - 2) / num_sma *
num_sma_max / (num_sma_max - 2)) / (1 - beta1 ** state['step'])
else:
step_size = group['lr'] / (1 - beta1 ** state['step'])
buffered[2] = step_size
if group['weight_decay'] != 0:
p_fp32.add_(p_fp32, alpha=-group['weight_decay'] * group['lr'])
# more conservative since it's an approximated value
if num_sma >= 5:
denom = exp_avg_sq.sqrt().add_(group['eps'])
p_fp32.addcdiv_(exp_avg, denom, value=-step_size)
else:
p_fp32.add_(exp_avg, alpha=-step_size)
p.copy_(p_fp32)
return loss
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