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"""
SGDP Optimizer Implementation copied from https://github.com/clovaai/AdamP/blob/master/adamp/sgdp.py
Paper: `Slowing Down the Weight Norm Increase in Momentum-based Optimizers` - https://arxiv.org/abs/2006.08217
Code: https://github.com/clovaai/AdamP
Copyright (c) 2020-present NAVER Corp.
MIT license
"""
import torch
import torch.nn as nn
from torch.optim.optimizer import Optimizer, required
import math
class SGDP(Optimizer):
def __init__(self, params, lr=required, momentum=0, dampening=0,
weight_decay=0, nesterov=False, eps=1e-8, delta=0.1, wd_ratio=0.1):
defaults = dict(lr=lr, momentum=momentum, dampening=dampening, weight_decay=weight_decay,
nesterov=nesterov, eps=eps, delta=delta, wd_ratio=wd_ratio)
super(SGDP, self).__init__(params, defaults)
def _channel_view(self, x):
return x.view(x.size(0), -1)
def _layer_view(self, x):
return x.view(1, -1)
def _cosine_similarity(self, x, y, eps, view_func):
x = view_func(x)
y = view_func(y)
x_norm = x.norm(dim=1).add_(eps)
y_norm = y.norm(dim=1).add_(eps)
dot = (x * y).sum(dim=1)
return dot.abs() / x_norm / y_norm
def _projection(self, p, grad, perturb, delta, wd_ratio, eps):
wd = 1
expand_size = [-1] + [1] * (len(p.shape) - 1)
for view_func in [self._channel_view, self._layer_view]:
cosine_sim = self._cosine_similarity(grad, p.data, eps, view_func)
if cosine_sim.max() < delta / math.sqrt(view_func(p.data).size(1)):
p_n = p.data / view_func(p.data).norm(dim=1).view(expand_size).add_(eps)
perturb -= p_n * view_func(p_n * perturb).sum(dim=1).view(expand_size)
wd = wd_ratio
return perturb, wd
return perturb, wd
def step(self, closure=None):
loss = None
if closure is not None:
loss = closure()
for group in self.param_groups:
weight_decay = group['weight_decay']
momentum = group['momentum']
dampening = group['dampening']
nesterov = group['nesterov']
for p in group['params']:
if p.grad is None:
continue
grad = p.grad.data
state = self.state[p]
# State initialization
if len(state) == 0:
state['momentum'] = torch.zeros_like(p.data)
# SGD
buf = state['momentum']
buf.mul_(momentum).add_(1 - dampening, grad)
if nesterov:
d_p = grad + momentum * buf
else:
d_p = buf
# Projection
wd_ratio = 1
if len(p.shape) > 1:
d_p, wd_ratio = self._projection(p, grad, d_p, group['delta'], group['wd_ratio'], group['eps'])
# Weight decay
if weight_decay != 0:
p.data.mul_(1 - group['lr'] * group['weight_decay'] * wd_ratio / (1-momentum))
# Step
p.data.add_(-group['lr'], d_p)
return loss
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