preparing for first release
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thomwolf
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pytorch_pretrained_bert/optimization.py
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pytorch_pretrained_bert/optimization.py
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# coding=utf-8
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# Copyright 2018 The Google AI Language Team Authors and The HugginFace Inc. team.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""PyTorch optimization for BERT model."""
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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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if x < warmup:
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return x/warmup
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return 0.5 * (1.0 + torch.cos(math.pi * x))
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def warmup_constant(x, warmup=0.002):
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if x < warmup:
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return x/warmup
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return 1.0
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def warmup_linear(x, warmup=0.002):
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if x < warmup:
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return x/warmup
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return 1.0 - 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 BERT version of Adam algorithm with weight decay fix (and no ).
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Params:
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lr: learning rate
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warmup: portion of t_total for the warmup, -1 means no warmup. Default: -1
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t_total: total number of training steps for the learning
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rate schedule, -1 means constant learning rate. Default: -1
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schedule: schedule to use for the warmup (see above). Default: 'warmup_linear'
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b1: Adams b1. Default: 0.9
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b2: Adams b2. Default: 0.999
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e: Adams epsilon. Default: 1e-6
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weight_decay_rate: Weight decay. Default: 0.01
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max_grad_norm: Maximum norm for the gradients (-1 means no clipping). Default: 1.0
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"""
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def __init__(self, params, lr, warmup=-1, t_total=-1, schedule='warmup_linear',
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b1=0.9, b2=0.999, e=1e-6, weight_decay_rate=0.01,
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max_grad_norm=1.0):
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if not lr >= 0.0:
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raise ValueError("Invalid learning rate: {} - should be >= 0.0".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 0.0 <= warmup < 1.0 and not warmup == -1:
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raise ValueError("Invalid warmup: {} - should be in [0.0, 1.0[ or -1".format(warmup))
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if not 0.0 <= b1 < 1.0:
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raise ValueError("Invalid b1 parameter: {} - should be in [0.0, 1.0[".format(b1))
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if not 0.0 <= b2 < 1.0:
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raise ValueError("Invalid b2 parameter: {} - should be in [0.0, 1.0[".format(b2))
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if not e >= 0.0:
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raise ValueError("Invalid epsilon value: {} - should be >= 0.0".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, weight_decay_rate=weight_decay_rate,
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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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if group['t_total'] != -1:
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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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else:
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lr_scheduled = group['lr']
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lr.append(lr_scheduled)
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return lr
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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['next_m'] = torch.zeros_like(p.data)
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# Exponential moving average of squared gradient values
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state['next_v'] = torch.zeros_like(p.data)
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next_m, next_v = state['next_m'], state['next_v']
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beta1, beta2 = group['b1'], group['b2']
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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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# In-place operations to update the averages at the same time
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next_m.mul_(beta1).add_(1 - beta1, grad)
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next_v.mul_(beta2).addcmul_(1 - beta2, grad, grad)
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update = next_m / (next_v.sqrt() + group['e'])
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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 group['weight_decay_rate'] > 0.0:
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update += group['weight_decay_rate'] * p.data
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if group['t_total'] != -1:
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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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else:
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lr_scheduled = group['lr']
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update_with_lr = lr_scheduled * update
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p.data.add_(-update_with_lr)
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state['step'] += 1
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# step_size = lr_scheduled * math.sqrt(bias_correction2) / bias_correction1
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# bias_correction1 = 1 - beta1 ** state['step']
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# bias_correction2 = 1 - beta2 ** state['step']
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return loss
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