utils.py

# coding=utf-8
# Copyright (c) 2020, NVIDIA CORPORATION.  All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Utilities for models."""

import math

import torch

from .transformer import LayerNorm


def init_method_normal(sigma):
    """Init method based on N(0, sigma)."""
    def init_(tensor):
        return torch.nn.init.normal_(tensor, mean=0.0, std=sigma)

    return init_


def scaled_init_method_normal(sigma, num_layers):
    """Init method based on N(0, sigma/sqrt(2*num_layers)."""
    std = sigma / math.sqrt(2.0 * num_layers)

    def init_(tensor):
        return torch.nn.init.normal_(tensor, mean=0.0, std=std)

    return init_


def get_linear_layer(rows, columns, init_method):
    """Simple linear layer with weight initialization."""
    layer = torch.nn.Linear(rows, columns)
    init_method(layer.weight)
    with torch.no_grad():
        layer.bias.zero_()
    return layer


@torch.jit.script
def gelu_impl(x):
    """OpenAI's gelu implementation."""
    return 0.5 * x * (1.0 + torch.tanh(0.7978845608028654 * x *
                                       (1.0 + 0.044715 * x * x)))
def openai_gelu(x):
    return gelu_impl(x)


def get_params_for_weight_decay_optimization(module):
    """Divide params into with-weight-decay and without-weight-decay groups.
    Layernorms and baises will have no weight decay but the rest will.
    """
    weight_decay_params = {'params': []}
    no_weight_decay_params = {'params': [], 'weight_decay': 0.0}
    for module_ in module.modules():
        if isinstance(module_, LayerNorm):
            no_weight_decay_params['params'].extend(
                [p for p in list(module_._parameters.values())
                 if p is not None])
        else:
            weight_decay_params['params'].extend(
                [p for n, p in list(module_._parameters.items())
                 if p is not None and n != 'bias'])
            no_weight_decay_params['params'].extend(
                [p for n, p in list(module_._parameters.items())
                 if p is not None and n == 'bias'])

    return weight_decay_params, no_weight_decay_params


def bert_attention_mask_func(attention_scores, attention_mask):
    attention_scores = attention_scores + attention_mask
    return attention_scores


def bert_extended_attention_mask(attention_mask, dtype):
    # We create a 3D attention mask from a 2D tensor mask.
    # [b, 1, s]
    attention_mask_b1s = attention_mask.unsqueeze(1)
    # [b, s, 1]
    attention_mask_bs1 = attention_mask.unsqueeze(2)
    # [b, s, s]
    attention_mask_bss = attention_mask_b1s * attention_mask_bs1
    # [b, 1, s, s]
    extended_attention_mask = attention_mask_bss.unsqueeze(1)
    # Since attention_mask is 1.0 for positions we want to attend and 0.0
    # for masked positions, this operation will create a tensor which is
    # 0.0 for positions we want to attend and -10000.0 for masked positions.
    # Since we are adding it to the raw scores before the softmax, this is
    # effectively the same as removing these entirely.
    # fp16 compatibility
    extended_attention_mask = extended_attention_mask.to(dtype=dtype)
    extended_attention_mask = (1.0 - extended_attention_mask) * -10000.0

    return extended_attention_mask


def bert_position_ids(token_ids):
    # Create position ids
    seq_length = token_ids.size(1)
    position_ids = torch.arange(seq_length, dtype=torch.long,
                                device=token_ids.device)
    position_ids = position_ids.unsqueeze(0).expand_as(token_ids)

    return position_ids