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