144 lines
5.7 KiB
Python
144 lines
5.7 KiB
Python
import math
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import torch
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from torch.optim import Optimizer
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from torch.nn.utils import clip_grad_norm_
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def warmup_cosine(x, warmup=0.002):
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s = 1 if x <= warmup else 0
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return s*(x/warmup) + (1-s)*(0.5 * (1 + torch.cos(math.pi * x)))
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def warmup_constant(x, warmup=0.002):
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s = 1 if x <= warmup else 0
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return s*(x/warmup) + (1-s)*1
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def warmup_linear(x, warmup=0.002):
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s = 1 if x <= warmup else 0
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return (s*(x/warmup) + (1-s))*(1-x)
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SCHEDULES = {
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'warmup_cosine':warmup_cosine,
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'warmup_constant':warmup_constant,
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'warmup_linear':warmup_linear,
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}
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class BERTAdam(Optimizer):
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"""Implements Open AI version of Adam algorithm with weight decay fix.
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"""
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def __init__(self, params, lr, schedule, warmup, t_total,
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b1=0.9, b2=0.999, e=1e-6, l2=0,
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vector_l2=False, max_grad_norm=-1, **kwargs):
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if not 0.0 <= lr:
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raise ValueError("Invalid learning rate: {}".format(lr))
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if schedule not in SCHEDULES:
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raise ValueError("Invalid schedule parameter: {}".format(schedule))
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if not 0 <= warmup:
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raise ValueError("Invalid warmup: {}".format(warmup))
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if not 0.0 <= b1 < 1.0:
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raise ValueError("Invalid b1 parameter: {}".format(b1))
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if not 0.0 <= b2 < 1.0:
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raise ValueError("Invalid b2 parameter: {}".format(b2))
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if not 0.0 <= e:
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raise ValueError("Invalid epsilon value: {}".format(e))
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defaults = dict(lr=lr, schedule=schedule, warmup=warmup, t_total=t_total,
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b1=b1, b2=b2, e=e, l2=l2, vector_l2=vector_l2,
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max_grad_norm=max_grad_norm)
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super(BERTAdam, self).__init__(params, defaults)
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def get_lr(self):
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lr = []
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for group in self.param_groups:
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for p in group['params']:
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state = self.state[p]
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if len(state) == 0:
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return [0]
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schedule_fct = SCHEDULES[group['schedule']]
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lr_scheduled = group['lr'] * schedule_fct(state['step']/group['t_total'], group['warmup'])
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lr.append(lr_scheduled)
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return lr
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def to(self, device):
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""" Move the optimizer state to a specified device"""
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for state in self.state.values():
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state['exp_avg'].to(device)
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state['exp_avg_sq'].to(device)
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def initialize_step(self, initial_step):
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"""Initialize state with a defined step (but we don't have stored averaged).
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Arguments:
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initial_step (int): Initial step number.
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"""
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for group in self.param_groups:
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for p in group['params']:
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state = self.state[p]
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# State initialization
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state['step'] = initial_step
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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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def step(self, closure=None):
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"""Performs a single optimization step.
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Arguments:
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closure (callable, optional): A closure that reevaluates the model
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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['b1'], group['b2']
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state['step'] += 1
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# Add grad clipping
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if group['max_grad_norm'] > 0:
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clip_grad_norm_(p, group['max_grad_norm'])
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# Decay the first and second moment running average coefficient
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exp_avg.mul_(beta1).add_(1 - beta1, grad)
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exp_avg_sq.mul_(beta2).addcmul_(1 - beta2, grad, grad)
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denom = exp_avg_sq.sqrt().add_(group['e'])
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bias_correction1 = 1 - beta1 ** state['step']
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bias_correction2 = 1 - beta2 ** state['step']
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schedule_fct = SCHEDULES[group['schedule']]
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lr_scheduled = group['lr'] * schedule_fct(state['step']/group['t_total'], group['warmup'])
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step_size = lr_scheduled * math.sqrt(bias_correction2) / bias_correction1
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p.data.addcdiv_(-step_size, exp_avg, denom)
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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 ot 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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if (len(p.size()) > 1 or group['vector_l2']) and group['l2'] > 0:
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p.data.add_(-lr_scheduled * group['l2'], p.data)
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return loss
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