113 lines
4.8 KiB
Python
113 lines
4.8 KiB
Python
"""
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AdamW optimizer (weight decay fix)
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copied from hugginface (https://github.com/huggingface/transformers).
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"""
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import math
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from typing import Callable, Iterable, Tuple
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import torch
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from torch.optim import Optimizer
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class AdamW(Optimizer):
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"""
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Implements Adam algorithm with weight decay fix as introduced in `Decoupled Weight Decay Regularization
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<https://arxiv.org/abs/1711.05101>`__.
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Parameters:
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params (:obj:`Iterable[torch.nn.parameter.Parameter]`):
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Iterable of parameters to optimize or dictionaries defining parameter groups.
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lr (:obj:`float`, `optional`, defaults to 1e-3):
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The learning rate to use.
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betas (:obj:`Tuple[float,float]`, `optional`, defaults to (0.9, 0.999)):
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Adam's betas parameters (b1, b2).
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eps (:obj:`float`, `optional`, defaults to 1e-6):
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Adam's epsilon for numerical stability.
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weight_decay (:obj:`float`, `optional`, defaults to 0):
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Decoupled weight decay to apply.
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correct_bias (:obj:`bool`, `optional`, defaults to `True`):
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Whether ot not to correct bias in Adam (for instance, in Bert TF repository they use :obj:`False`).
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"""
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def __init__(
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self,
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params: Iterable[torch.nn.parameter.Parameter],
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lr: float = 1e-3,
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betas: Tuple[float, float] = (0.9, 0.999),
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eps: float = 1e-6,
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weight_decay: float = 0.0,
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correct_bias: bool = True,
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):
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if lr < 0.0:
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raise ValueError("Invalid learning rate: {} - should be >= 0.0".format(lr))
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if not 0.0 <= betas[0] < 1.0:
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raise ValueError("Invalid beta parameter: {} - should be in [0.0, 1.0[".format(betas[0]))
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if not 0.0 <= betas[1] < 1.0:
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raise ValueError("Invalid beta parameter: {} - should be in [0.0, 1.0[".format(betas[1]))
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if not 0.0 <= eps:
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raise ValueError("Invalid epsilon value: {} - should be >= 0.0".format(eps))
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defaults = dict(lr=lr, betas=betas, eps=eps, weight_decay=weight_decay, correct_bias=correct_bias)
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super().__init__(params, defaults)
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def step(self, closure: Callable = None):
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"""
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Performs a single optimization step.
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Arguments:
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closure (:obj:`Callable`, `optional`): A closure that reevaluates the model and returns the loss.
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"""
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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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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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if grad.is_sparse:
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raise RuntimeError("Adam does not support sparse gradients, please consider SparseAdam instead")
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state = self.state[p]
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# State initialization
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if len(state) == 0:
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state["step"] = 0
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# Exponential moving average of gradient values
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state["exp_avg"] = torch.zeros_like(p.data)
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# Exponential moving average of squared gradient values
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state["exp_avg_sq"] = torch.zeros_like(p.data)
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exp_avg, exp_avg_sq = state["exp_avg"], state["exp_avg_sq"]
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beta1, beta2 = group["betas"]
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state["step"] += 1
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# Decay the first and second moment running average coefficient
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# In-place operations to update the averages at the same time
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exp_avg.mul_(beta1).add_(grad, alpha=1.0 - beta1)
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exp_avg_sq.mul_(beta2).addcmul_(grad, grad, value=1.0 - beta2)
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denom = exp_avg_sq.sqrt().add_(group["eps"])
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step_size = group["lr"]
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if group["correct_bias"]: # No bias correction for Bert
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bias_correction1 = 1.0 - beta1 ** state["step"]
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bias_correction2 = 1.0 - beta2 ** state["step"]
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step_size = step_size * math.sqrt(bias_correction2) / bias_correction1
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p.data.addcdiv_(exp_avg, denom, value=-step_size)
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# Just adding the square of the weights to the loss function is *not*
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# the correct way of using L2 regularization/weight decay with Adam,
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# since that will interact with the m and v parameters in strange ways.
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#
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# Instead we want to decay the weights in a manner that doesn't interact
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# with the m/v parameters. This is equivalent to adding the square
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# of the weights to the loss with plain (non-momentum) SGD.
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# Add weight decay at the end (fixed version)
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if group["weight_decay"] > 0.0:
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p.data.add_(p.data, alpha=-group["lr"] * group["weight_decay"])
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return loss
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